edge.rit.eduedge.rit.edu/content/OldEDGE/public/Archives/P05512/PDR.doc · Web viewIn spite of what figure (3.9) may look like, the data can be successfully demodulated and stored

Preliminary Design ReviewNovember 12, 2004

Team 05512Brian Gonzales

Naanzem HoomkwapWilliam Lambert

Surat Teerakapibal

Department of Electrical EngineeringKate Gleason College of Engineering

Rochester Institute of Technology76 Lomb Memorial Drive

Rochester, NY 14623-5604

Executive Summary

Modern cars frequently come equipped with remote keyless entry systems. These

systems allow the automobile owner to perform a variety of tasks, including unlocking

doors, opening doors, opening trunks, arming alarms, and setting off panic alarms from a

maximum distance of 15 to 100 feet. Secondary uses for these systems have evolved as

their presence has become ever more ubiquitous. One such application is in locating a

vehicle lost in a parking lot – the automobile owner presses the “lock” or “panic” button,

causing the car horn to emit a beep. The user is then directed by sound to his or her car.

Some of these RKE applications benefit from a range which exceeds many of the

standard systems. The purpose of this project is to implement a non-intrusive method of

extending existing RKE systems ranges. In order to accomplish this, several versions of

repeaters are proposed. The advantages and disadvantages of each approach are

discussed, and a design for the circuitry is developed.

After feasibility assessments, an approach which could repeat RKE systems for a

wide variety of cars was developed. A receiver is implemented with high performance

components. A microcontroller then detects the incoming digital data at a much higher

rate than is being sent. The data is filtered then stored. When the end of the transmission

is detected, the microcontroller activates a small transmitter which repeats the signal to

the car.

The system developed in this paper will function for all RKE systems operating in the

315 MHz band using ASK modulation (covering most cars in the US). The system is

compact, battery powered, and requires no connections to the automobile that will

contain it.

05512 RKE Repeater 2

1. INTRODUCTION...............................................................................................................................7

1.1 BACKGROUND................................................................................................................................81.1.1 RKE Systems..................................................................................................................................81.1.2 Repeater Systems...........................................................................................................................9

1.2 PROJECT DESCRIPTION.........................................................................................................................101.3 PROJECT OBJECTIVE.............................................................................................................................101.4 PROJECT SCOPE....................................................................................................................................111.5 FUNDING..............................................................................................................................................11

2. SPECIFICATIONS..................................................................................................................................12

2.1 ANTENNA SPECIFICATIONS..................................................................................................................122.2 RECEIVER SPECIFICATIONS..................................................................................................................122.3 TRANSMITTER SPECIFICATIONS............................................................................................................132.4 CONTROL SPECIFICATIONS...................................................................................................................132.5 HOUSING SPECIFICATIONS...................................................................................................................142.6 LEGAL SPECIFICATIONS.......................................................................................................................15

3. CONCEPT DEVELOPMENT................................................................................................................16

3.1 ANTENNA.............................................................................................................................................163.1.1 Antenna Theory............................................................................................................................163.1.2 Antenna Simulation......................................................................................................................19

3.2 RECEIVER.............................................................................................................................................233.2.1 Receiver Theory...........................................................................................................................233.2.2 Receiver Possibilities...................................................................................................................27

3.3 REPEATER.............................................................................................................................................283.4 TRANSMITTER......................................................................................................................................323.5 FILTERS................................................................................................................................................34

3.5.1 Preselector...................................................................................................................................343.5.2 Intermediate Frequency Filter.....................................................................................................353.5.3 Transmitter Output Filter............................................................................................................353.5.4 Filter Designs...............................................................................................................................353.5.5 Active Filters................................................................................................................................363.5.6 Passive Filters..............................................................................................................................363.5.7 SAW Filters..................................................................................................................................40

3.6 SYSTEM CONTROL................................................................................................................................413.7 HOUSING..............................................................................................................................................42

4. FEASIBILITY ASSESSMENT...............................................................................................................43

4.1 ANTENNA.............................................................................................................................................434.2 RECEIVER.............................................................................................................................................434.3 REPEATER.............................................................................................................................................474.4 TRANSMITTER......................................................................................................................................494.5 FILTERS................................................................................................................................................51

4.5.1 Preselector...................................................................................................................................514.5.2 Intermediate Frequency Filter.....................................................................................................524.5.3 Transmitter Output Filter............................................................................................................53

4.5 CONTROLLER........................................................................................................................................544.6 REPEATER HOUSING.............................................................................................................................54

5. ANALYSIS AND DESIGN......................................................................................................................56

5.1 ANTENNA DESIGN................................................................................................................................575.2 RECEIVER DESIGN................................................................................................................................59

5.2.2 Low Noise Amplifier....................................................................................................................605.2.3 Mixer and IF Preamp...................................................................................................................60


5.2.4 IF Limiting Amplifier with RSSI..................................................................................................615.3 TRANSMITTER......................................................................................................................................635.4 FILTERS................................................................................................................................................68

5.4.1 Preselector...................................................................................................................................685.4.2 Intermediate Frequency Filter.....................................................................................................695.4.3 Transmitter Output Filter............................................................................................................70

5.5 T/R SWITCH..........................................................................................................................................715.6 HOUSING DESIGN.................................................................................................................................725.7 CONTROL SYSTEM DESIGN..................................................................................................................755.8 IMPEDANCE MATCHING NETWORK......................................................................................................92

6. WORK COMPLETED............................................................................................................................93

BIBLIOGRAPHY.........................................................................................................................................97

APPENDIX A – FCC REGULATIONS.....................................................................................................99

APPENDIX B – BILL OF MATERIALS................................................................................................101

APPENDIX B – BILL OF MATERIALS................................................................................................101

Appendix C – Complete Circuit Schematic.................................................................................................102


Table of FiguresTABLE 2.1: CONTROLLER RESPONSIBILITIES..................................................................................................14FIGURE 3.1: MININEC PROGRAM USED FOR ANTENNA MODELING...............................................................20FIGURE 3.2: RADIATION PATTERN OF ¼ WAVE DIPOLE..................................................................................21FIGURE 3.3: DIRECTIVE GAIN PATTERN OF THE QUARTER WAVE ANTENNA.................................................22FIGURE 3.4: CURRENT DISTRIBUTION OF THE QUARTER WAVE ANTENNA.....................................................23TABLE 3.1: ELECTRICAL CHARACTERISTICS FOR A QUARTER WAVE ANTENNA.............................................23TABLE 3.2: IMPORTANT MIXER PARAMETERS [RF DESIGN GUIDES]............................................................26TABLE 3.3: RECEIVER IC POSSIBILITIES........................................................................................................27FIGURE 3.6: DIGITAL WAVEFORM (ABOVE) AND CARRIER (BELOW) WHICH COMPRISE THE SIGNAL FOR ASK

...............................................................................................................................................................30FIGURE 3.7: EXAMPLE OF ASK MODULATION OF THE SEQUENCE “1 0 1 0 1 1 0 0”.....................................30FIGURE 3.8: SIGNAL CORRUPTED BY GAUSSIAN NOISE.................................................................................31FIGURE 3.9: SIGNAL AFTER GOING THROUGH THE ENVELOPE DETECTOR......................................................32FIGURE 3.10: TRANSMITTER BLOCK DIAGRAM...............................................................................................33TABLE 3.4: TRANSMITTER IC POSSIBILITIES..................................................................................................34FIGURE 3.11: A PASSIVE BANDPASS FILTER....................................................................................................37FIGURE 3.12: FREQUENCY RESPONSE OF A PASSIVE BANDPASS FILTER.........................................................37FIGURE 3.13: SOME LOWPASS IF FILTERS......................................................................................................38FIGURE 3.14: FREQUENCY RESPONSE OF VARIOUS IF LOWPASS FILTERS.......................................................38FIGURE 3.15: SOME TRANSMITTER PA LOW PASS FILTERS FOR DIFFERENT CUTOFF FREQUENCIES.............39FIGURE 3.16: FREQUENCY RESPONSE OF THE TRANSMITTER LOW PASS FILTERS...........................................39FIGURE 3.17: SAW FILTER.............................................................................................................................40FIGURE 3.18: SAW FILTER IMPEDANCE MATCHING......................................................................................41TABLE 4.1: WEIGHTED ANTENNA FEASIBILITY ANALYSIS..............................................................................43TABLE 4.2: FEASIBILITY ANALYSIS OF THE RECEIVER....................................................................................47TABLE 4.3: FEASIBILITY ASSESSMENT FOR THE REPEATER............................................................................49TABLE 4.4: FEASIBILITY ASSESSMENT FOR THE TRANSMITTER......................................................................51TABLE 5.1: ESTIMATED POWER DRAW FOR CIRCUITRY..................................................................................56TABLE 5.2: LINK BUDGET ANALYSIS.............................................................................................................57FIGURE 5.1: DIRECTIVE GAIN PATTERN OF THE QUARTER WAVE ANTENNA.................................................58FIGURE 5.2: CURRENT DISTRIBUTION OF THE QUARTER WAVE ANTENNA.....................................................58TABLE 5.3: ELECTRICAL CHARACTERISTICS FOR A QUARTER WAVE ANTENNA.............................................59FIGURE 5.3: THE FINAL ANTENNA DESIGN......................................................................................................59FIGURE 5.4: RFRD0420 PIN DIAGRAM...........................................................................................................60FIGURE 5.5: FULL RECEIVER SCHEMATIC......................................................................................................62FIGURE 5.6: TRANSMITTER SCHEMATIC.........................................................................................................63FIGURE 5.7: TRANSMITTER OUTPUT CIRCUITRY............................................................................................64FIGURE 5.8: SIMULATION OF TRANSMITTER OUTPUT CIRCUITRY.................................................................64TABLE 5.2: MAX1472 PIN DESCRIPTION.......................................................................................................66FIGURE 5.9: COMPLETE TRANSMITTER SCHEMATIC.......................................................................................67FIGURE 5.11: SAW FILTER FREQUENCY RESPONSE.......................................................................................69FIGURE 5.12: INTERMEDIATE FREQUENCY LOW PASS FILTER.......................................................................69FIGURE 5.13: IF FILTER FREQUENCY RESPONSE............................................................................................70FIGURE 5.14: TRANSMITTER OUTPUT FILTER.................................................................................................70FIGURE 5.15: TRANSMITTER FILTER FREQUENCY RESPONSE.........................................................................71FIGURE 5.16: TRANSMITTER/RECEIVER SWITCH............................................................................................72TABLE 5.4: ADG918 PIN DESCRIPTION..........................................................................................................72FIGURE 5.17: SPECIFICATIONS FOR THE HOUSING..........................................................................................74TABLE 5.5: CONTROL SYSTEM SPECS [MICROCHIP]......................................................................................76TABLE 5.6: CONNECTIONS NEEDED FOR MICROCONTROLLER.......................................................................76TABLE 5.7: PIN CONNECTIONS TO THE MICROCONTROLLER [MICROCHIP]....................................................77FIGURE 5.18: PIC16F87 MICROCONTROLLER SCHEMATIC DIAGRAM...........................................................78FIGURE 5.19: HIGH LEVEL OVERVIEW OF CONTROL SYSTEMS......................................................................79TABLE 5.8: PIN STATES AT POWER ON...........................................................................................................80


FIGURE 5.20: POWER ON SEQUENCE..............................................................................................................81FIGURE 5.21: INTERRUPT HANDLING FOR CHANGE ON RB4...........................................................................82FIGURE 5.22: ROUTINE TO CHECK FOR VALID RECEIVED DATA AND ENTER RECEIVE MODE.........................84FIGURE 5.23: RATE INDEPENDENT DETECTION OF THE ASK SIGNAL.............................................................86FIGURE 5.24: ROUTINE FOR RECEIVING VALID DATA.....................................................................................87FIGURE 5.25: EXAMPLE OF CORRUPTED DATA...............................................................................................88FIGURE 5.26: THE BINARY FILTERING SUBROUTINE.......................................................................................89FIGURE 5.27: THE TRANSMIT ROUTINE...........................................................................................................91FIGURE 5.28: IMPEDANCE MATCHING NETWORK............................................................................................92FIGURE 6.2: TANK FILTER..............................................................................................................................94FIGURE 6.3: TANK FILTER FREQUENCY RESPONSE........................................................................................94Figure 6.4: First Generation Receiver Schematic...........................................................................................95


1. Introduction

A large percentage of automobiles manufactured in the last 15 years have come

equipped with Remote Keyless Entry (RKE) systems. These systems allow the owner of

the automobile to perform basic functions such as locking the automobile, unlocking the

automobile, opening the trunk, starting the car, opening doors, setting alarms, or even

setting off a panic alarm by pressing a button of a remote control. The remote control is

often a small device attached to the keychain called a “key fob”. Having the ability to

perform these functions remotely allows the user to open a car quickly if needed, open a

trunk if his hands are full, unlock doors for everyone so they do not have to wait around

in inclement weather, and so on. Because of the usefulness of these features, RKE

systems have become nearly ubiquitous.

In addition to their intended functions, RKE systems have become commonly used as

locator devices for automobiles in parking lots. If an owner leaves his or her car at the

mall and can remember the general location of the car, he or she can press the “lock” or

“panic” functions, causing the automobile to sound the horn. This can greatly aid the user

in finding his or her car.

RKE systems are often implemented in lowest cost and least obtrusive manner

possible. Because of this, the systems on some automobiles are restricted to a very short

range, down to 15 feet, while others will function up to and over 100 feet. Sometimes, the

short range of the systems can be an unfortunate limiter to their utility. For instance,

someone looking for his or her car might want to be able to sound the horn from a

distance away. People with car alarms which go off frequently might want to be able to

turn them off without walking all the way out to their car.


Such applications make extending the range of the repeater desirable. There are

obvious ways of doing this, for instance modifying the car to have a better antenna for the

RKE device. However, the average user does not necessarily want to modify his or her

car to improve RKE performance. Instead, a non-intrusive way of extending an RKE

systems range is desired. The best solution for to this problem was determined to be an

RKE repeater. The repeater would have a high performance antenna and receiver capable

of substantial gain over the system included in the automobile. The repeater would listen

for a transmission, store it, and then retransmit it to the car, allowing the car to perform

the requested operation. In this way, the range of the system could be transparently

extended with no modifications to the automobile required.

By using careful design, a cost effective, marketable product could be produced that

could ultimately be sold at an electronics store. If the range extension is significant, the

product would be useful to a wide range of consumers looking for the added advantages

of a more robust RKE system.

1.1 Background

1.1.1 RKE Systems

RKE systems generally communicate in an unlicensed portion of the spectrum

reserved for intermittent transmission of control data. This frequency is typically 315.0

MHz for US systems and 433.92 MHz for European systems. They key fob is generally

an extremely low power device, on the order of 1 mW.

When a key is pressed on the key fob, it translates it into a digital code of a few bits

in length. This code is combined with a pseudo-random hopping code (for security


purposes). The whole code is then modulated into a radio signal, most often using

amplitude shift keying (ASK) modulation. Upon receipt of a transmission, the vehicle

verifies the security code and then executes the command.

The code that is sent has a random part and a fixed part. The fixed part of the code

tells the vehicle what function to implement. The random part is used by the vehicle to

verify that the signal it is receiving is from the owner and not from someone else’s key

fob. The key fob and the vehicle both have random number generators that are seeded the

same. The vehicle stores the next 256 possible numbers and checks to see of the signal

sent has one or those numbers. If it does, then the vehicle will respond to the signal. If it

does not, then receiver ignores the signal. The random code ensures that vehicle does not

respond to anything other then the owner’s key fob.

1.1.2 Repeater Systems

A repeater is a device used in communication systems to extend the range of an

existing communication system. Repeaters are used often in today’s wide cell phone

networks and radio networks. Repeater stations and towers are common throughout the

United States. Because of this there are a wide range of standard repeater designs. These

designs all have the same basic process - a signal is received through an antenna, the

frequency of the signal is shifted, and the signal is retransmitted through the same

antenna.

If the signal in a standard repeater system is not shifted it would be impossible to

simultaneously receive and then retransmit the signal through the same antenna because

the power out of the transmitter would overload the receiver. The receiver for the repeater


and the transmitter for the receiver must be isolated. Both the receiver and the transmitter

will have a narrow bandpass filter in front of them (called a duplexer). As long as the

output signal is shifted enough to be attenuated by the receivers filter, then there will be

sufficient isolation between the receiver and the transmitter. Without sufficient isolation

there will be positive feedback in the repeater.

If retransmission is on the same frequency, two approaches may be used. First, two

highly isolated antennas may be used. In such a system, the gain of the repeater must not

exceed the isolation between the antennas. In the second system, the signal is recorded

until the end is reached. Once the end is reached, the signal is transmitted again. This is

called a “Parrot” repeater. According to FCC regulations, such a device is not a repeater.

1.2 Project Description

Existing RKE systems work at ranges between 15 and 100 feet. This purpose of this

project is extend the range of the existing RKE system by designing a repeater that will

receive the signal from the key fob and retransmit it to the vehicle’s receiver. The range

of RKE systems should be extended to greater than 200 feet. To do this, the repeater must

be able to receive the signal from the key fob at a greater range then vehicle and then be

able to rapidly retransmit that signal to the vehicle.

1.3 Project Objective

An affordable RKE repeater capable of extending the range of existing RKE systems

with out modification to the automobile will be constructed. The repeater will be

independent of the vehicle and the existing RKE system, including the power supply. The


device will be small, inexpensive, easily transferable between automobiles, and work

with most existing systems.

1.4 Project Scope

The scope of the project will be limited to systems functioning on 315 MHz using

ASK modulation. Other types of RKE systems will not be covered by the repeater.

1.5 Funding

According to the financial constraint specified by the sponsor, the RF repeater is

expected to have a competitive price in its market, determined by the developer to be

$30-50. A total of $200.00 has been committed by the sponsor for the development of the

product. More funds are available if needed.

For the prototype, the antenna will require approximately $20 since the only

connectors would need to be purchased. Mixers, filters and housing for the receivers were

purchased for roughly $80 in order to conduct preliminary test circuits. These parts will

also be used when building the prototypes. The controller part of the prototype should

cost about $10 if a programmer does not need to be purchased. The rest of the funds

would be allocated towards the receiver and transmitter circuitry.


2. Specifications

2.1 Antenna Specifications

The antenna required for this project needs to be omni-directional (radiating

equally well in all directions in one plane), based on the assumption that the user is not

going to be using the device from an elevation significantly above or below the vehicle.

The design frequency for this project is assumed to be 315MHz, which means that the

wavelength is 0.952m. For this wavelength, many different antennas can be considered,

such as the quarter or half wave dipole, the helix antenna, and the loop antenna among

others.

2.2 Receiver Specifications

The chief requirement for the RKE repeater is that it be able to receive and retransmit

all RKE devices. RKE devices on cars in the United States operate primarily in two

bands: at 315MHz (American/Japanese cars) and 433MHz (European cars). The repeater

will only be able to function at one of these frequencies at a time, so the receiver will be

designed accordingly.

In order for the receiver to function for all the different available RKE systems, it

must be capable of receiving and retransmitting different modulation types at different

data rates. The two modulation types that are likely to be encountered are ASK and FSK.

These two modulations types are very different – because of this the receiver must be

limited to recovering one or the other. Research indicates that the vast majority of RKE

systems use ASK, therefore the receiver will be designed to detect ASK.


2.3 Transmitter Specifications

Because of the proximity of the repeater to the car’s receiver, very few requirements

are placed on the transmitter. It is merely required to transmit an ASK signal over a range

for a couple of feet to the automobile’s receiver. The transmitter must be a low power

device and capable of transmission at sufficient speed.

2.4 Control Specifications

For all repeater designs in which the repeater does not continuously retransmit

constantly, some sort of control unit is necessary. The controller will be responsible for

activating and deactivating the different portions of the circuit. When no signal is

incoming, the controller must keep the receiver turned on and listening while keeping

itself in a minimum power draw state.

When a valid transmission is being received, the controller must ensure that the data

from the transmission is being captured and stored in memory. After this, the controller

must activate the transmitter and send the data.

The power management done by the controller is crucial in making the final product

marketable – if the power consumption is too high for AA batteries, the repeater will

either have an unnecessarily short lifetime or will require more sizeable batteries.


Controller Responsibilities

1. Power Management

2. T/R Switch operation

3. Received data detection or A/D conversion

4. Data storage

5. Transmitter/Receiver operation

Table 2.1: Controller Responsibilities

2.5 Housing Specifications

In order for the RKE to be an effective consumer product, some amount of thought

must go into its physical form. It should be very small (consumers are unlikely to

purchase something that would prove unsightly in their expensive cars), easy to insert and

remove, and look attractive. Because a high quality antenna will be one of the best ways

of improving the range of the system, it is necessary that an attractive enclosure that still

facilitates the antenna to be designed.

The design specifies that the unit must be completely independent of the automobile

it will be used in. It must require no installation other than placing it appropriately in the

car and it must require no connections to the automobile. These requirements lead to the

following list of specifications for the housing:

1. Must contain room for batteries (preferably a standard size, such as AA or AAA).

2. Must not exceed 6” in length or width, excepting the antenna.


The housing should also facilitate its final placement. The only known specification

for placement of the unit at this time is that it should be above the window level.

2.6 Legal Specifications

The operation of the repeater within the United States is subject to FCC regulations,

Title 47, Chapter 1, Part 15, Section 231 – Periodic Operation including the band of the

repeaters operation. It specifies, “The provisions of this section are restricted to periodic

operation within the band 40.66-40.70 MHz and above 70 MHz. Except as shown in

paragraph (e) of this section, the intentional radiator is restricted to the transmission of a

control signal such as those used with alarm systems, door openers, remote switches,

etc.” [47CFR15.231].

The use of a repeater is not specifically granted by the FCC regulations. However, so

long as adequate circuitry is included in the design to ensure that the repeater does not

continuously transmit noise, no rules are being broken.

The rules govern maximum transmitted field strength. The transmission, however,

will only be going from the repeater to the receiver in a car, a distance that will, in the

worst case scenario of a minivan, not exceed a couple of meters. In order to best

conserve power the transmitter will operate at an extremely low voltage so the field

strength limitations will not be a concern.

It is likely that the device would require FCC approval in order to go to market. This

step should be taken in tandem with the rest of the design process in order to ensure that

no legal issues are encountered. Should legal issues be encountered, no part of the current

design would be usable for the system.


3. Concept Development

3.1 Antenna

Available antenna designs include the loop, the quarter wave antenna, and the half

wave antenna. In the case of the loop, the input impedance is in the order of a few

thousand ohms; unfortunately a loop doesn't offer a good impedance match to a coaxial

transmission line. Using two identical loops side by side with a few inches spacing

between them reduces the impedance. Space does not permit this though. The directional

pattern becomes asymmetrical and the nulls off the side may be only a few dB down from

the peak of the radiation pattern. An unbalanced, unshielded loop can also pick up

conducted interference from the feed line. The half wave antenna is similar to the quarter-

wave and even though the half-wave antenna's impact on installation is minimal, it is

taller than a quarter-wave antenna cut for the same frequency.

3.1.1 Antenna Theory

For theoretical purposes a finite length dipole will be analyzed to find the radiation

characteristics. It will be assumed that the dipole has a negligible diameter smaller than

the operating wavelength. Hence the current distribution for this dipole can be described

by the following equations:

(3.1.1)

Using the far field approximations given by the equation below,


(3.1.2)

Where,

dz’ = length of an infinitesimal dipole

The electric field can be obtained by integration.

(3.1.3)

The resulting expression for the electric field takes the form of

(3.1.4)

Using the relationship between E and H, H can be found and can be written as

(3.1.5)

Since a quarter wave dipole is being examined l can be replaced by /4 and k= 2/ in

equation (3.1.4).

The quarter wave antenna was simulated using EXPERT MININEC, an engineering

tool for the design and analysis of wire antennas. MININEC’s solution is based on the

numerical solution of an integral equation representation of electric fields given in

equation (3.1.4) above. MININEC assumes that the wire radius is very small with respect


to the wavelength and the wire length and the wire must be subdivided into short

segments so the radius is assumed small with respect to segment lengths. MININEC

makes use of the boundary condition on tangential electric field at the surface of a perfect

conductor, namely that the electric field must be zero. Based on the initial assumptions

that the wires must be thin, the total axial electric field on the wire is forced to zero. The

three sources of the tangential electric field on the wire are:

Currents and charges on the wires and on nearby wires.

Incoming waves from distance or nearby radiators.

Local sources of electric field on the wire.

Voltage sources or current sources are local sources that connect to the wires.

MININEC uses the moment method (MM) solution, which is a numerical procedure

for solving electric field integral equation. An important step in the MM is the choice of

basis functions; basis functions are chosen to represent the unknown currents. The

triangular basis function also known as the piecewise linear function is chosen in this

case. The piecewise linear function is defined by

(3.1.6)

Testing functions are also chosen to enforce the integral equation on the surface of the

wire [Antenna Theory]. A typical but not unique inner product is given by

(3.1.7)


Where the weighting testing function is represented by w in the equation above and S

is the surface of the structure to be analyzed. With the choice of basis and testing

functions, a matrix approximating the integral is defined. To achieve the matrix a set of N

testing functions {wm} = w1, w2…wN are defined in the domain of the operator. If this

matrix is inverted and multiplied by the local sources of electric field, the complex

magnitudes of the current basis functions are derived.[Antenna Theory]

3.1.2 Antenna Simulation

To run MININEC for a complete analysis of the current, impedance and radiation

patterns of the quarter wave antenna some parameters have to be defined.

Figure 3.1: MININEC Program used for antenna modeling


The antenna is placed on the z-axis as shown in the figure above and fed at the end of

the antenna at z =0. The antenna is simulated on a ground plane, because it is going to be

mounted on the metal top of the housing unit. The ground plane is also used to limit the

downward radiation of the antenna.

Given that the repeater is transmitting and receiving at 315MHz the wavelength can

be obtained as thus

(3.1.8)

The length therefore is quarter of the wavelength resulting in l = 0.238m. After a few

iterations the length had to be changed to get the optimal impedance and gain, the

optimum length was found to be 0.226m. Two geometry points are then defined as (x1, y1,

z1)=(0, 0, 0) and (x2, y2, z2)=(0, 0, 0.226). The method of moments requires that the wire

be broken into segments, the greater the number of segments the more accurate the result.

The number of segments for this antenna was set to 40; the points at which the different

segments of the wire are connected are identified as current nodes. The program was then

run to obtain the following results.


Figure 3.2: Radiation pattern of ¼ wave dipole

The Radiation pattern, which is a “mathematical function or a graphical

representation in this case of the radiation properties of the antenna as a function of space

coordinates”. The radiation pattern seen in figure 2 above sweeps from 0 and from

0 because the antenna is on a ground plane half of the radiation pattern is not

shown.

There are two measurements of gain, namely directive gain and power gain.

Directive gain is the ratio of the power density radiated in a particular direction to the

power density radiated to the same point by a reference antenna, assuming both antennas

are radiating the same amount of power. The power gain is the same as directive gain

except that antenna efficiency is taken in to account and the total power fed to the

antenna is used in the calculations. It is assumed that the antenna and the reference have

the same input power and the reference is lossless [Antenna Theory]. The power gain is

equal to the directive gain if an antenna is lossless (it radiates 100% of the input power).

The gain of an antenna is often used as a figure of merit. For the quarter-wave antenna


the as obtained from the simulation is seen the figure below, with the maximum at

5.15dB.

Figure 3.3: Directive Gain pattern of the Quarter wave antenna


Figure 3.4: Current distribution of the quarter wave antenna

Freq(MHz)

Resistance()

Reactance()

Impedance()

Phase(Deg)

VSWRdB

S11dB

S12dB

315 35.789 -.79302 35.798 -1.27 1.3978 -15.603 -1.5756

Table 3.1: Electrical characteristics for a quarter wave antenna

Technically, antenna impedance is the ratio at any given point in the antenna of

voltage to current at that point. Depending upon height above ground, the influence of

surrounding objects and other factors, a quarter-wave antenna with perfect ground

exhibits a nominal input impedance of around 36 ohms [A.R.R.L Antenna Book], which

is pretty close to the value seen in the table above.

3.2 Receiver

3.2.1 Receiver Theory

After the signal is received from the antenna, it is passed to the first filter. This

particular filter is known as the preselector. The preselector is designed to limit the

bandwidth of spectrum reaching the RF amplifier and mixer to minimize distortion. The

receiver spurious responses can also be attenuated using the preselector. The preselector

must also be able to suppress local oscillator energy originating in the receiver. A

possibility of the RF preselector filter is a highly selective, cavity tuned filter, cascaded

with a low-pass filter. As this filter will encounter the highest RF levels, it should possess

a high intercept point.

The RF amplifier is required to mainly isolate filter 1 and filter 2 from each other in

order to maintain the overall selectivity. Due to this fact, a high reverse isolation


amplifier is necessary. Other characteristics of the RF amplifier such as the noise figure,

gain and intercept point are determined by the receiver performance requirements.

The received signal is then passed to another filter, Filter 2. It is usually called the

image filter because of its nature to rejects image noise. This filter attenuates the receiver

spurious response frequencies, direct IF frequency pickup and noise at the image

frequency caused by the RF amplifier. The second harmonic occurred in the RF amplifier

and local oscillator energy leaking back to the antenna can also be suppressed by this

filter. Moreover, due to the fact that the mixer usually has very little rejection for odd

harmonics of the receive frequency that may leak to the system, it is extremely important

for this filter to not have any return responses at high frequencies.

To further maximize the intercept performance, a diplexer network can be added in

order to reject any signals that would reflect back into the mixer. This network has the

ability to suppress the local oscillator harmonics that might disturb the functionality of

the mixer.

Due to the fact that the LO signal has to have a relatively high amplitude, the mixer

will generate its own harmonics as it operates. As a result, double balanced mixer should

be used since they are internally balanced and so would not cause this particular problem.

To improve the mixer performance through optimizing the second-order intercept point,

externally generated second harmonics of the LO signal should be suppressed using the

injection filter.

The receiver’s channel selectivity is determined by the single-sideband (SSB) phase

noise of the first local oscillator. It can also be affected by the wideband noise which is

measured at the frequency offsets that are greater than the SSB phase noise. In addition, it


is very crucial to have a slow spurious signals in the LO signal to prevent the

corresponding receiver spurious responses. A LO synthesizer can be used to limit the

circuit block for frequency change lock time. As the LO signal is very significant to the

system performance as a whole, it must be able to oscillate regardless of temperature and

power supply variations.

After the signal is mixed, it is then passed to the first IF stage. The function of this

filter is to protect the following stages from close-in IM signals. It also has to provide

adjacent channel selectivity and attenuates the second image. Although two different

characteristics of the filter must be met, the number of poles required is determined by

the required second-image selectivity. This is due to the fact that the requirement on the

second-image selectivity is much more stringent than that of the adjacent channel

selectivity. The equivalent noise bandwidth of the IF chain is also a very important

receiver property as it determines the level of noise that reach the detector and the

modulation bandwidth that can be received. Group delay must also be compensated by

either software or hardware in order to minimize the group delay distortion. To improve

mixer’s IM performance, the maximum impedance presented to the high impedance

mixer on the filter skirts must be limited. This can be done by isolating the filter from the

mixer by an impedance inverter network. It is very crucial to select the first IF crystal

with a good IM.

Another high gain stage is then followed. This IF amplifier should possess a high

intercept point. However, if the earlier mentioned IF filter stage is present, the required

intercept point does not necessary have to be as high. [RF Design Guides]


Mixer Parameter Affected Receiver SpecificationConversion loss Receiver sensitivityThird-order intercept point Intermodulation distortionSecond-order intercept point Half IF spurious response rejectionHigher-order intercept point High-order spurious rejectionNoise balance Receiver sensitivity, AM noise rejectionLO to RF isolation Conducted LO energy propagating toward

antennaRF to IF isolation Susceptibility to direct IF frequency pickup

Table 3.2: Important Mixer Parameters [RF Design Guides]

Receiver Design Procedures

1. Allocate approximate gains and losses as needed to meet the required receiver

sensitivity specification and IM distortion requirements.

2. Select the first IF frequency.

3. Select the first LO injection side.

4. Investigate the mixer.

5. Based on mixer performance, design the injection filter and select LO technology.

6. Investigate filter topologies

7. Design the RF amplifier

Figure 3.5: Basic Receiver Design

05512 RKE Repeater

Filter # 1 Filter # 2

RF Amplifier

Injection Filter

1st IF Stages

1st IF Amplifier

Detector

1st Local Oscillator

26

3.2.2 Receiver Possibilities

The receiver can be built using discrete parts that meet the specifications as noted in

an earlier section. Although discrete parts were used in order to support the preliminary

assumption, existing receiver integrated circuit chips would reduce the cost in the final

prototype assembly. Further detailed discussions will be made in the Feasibility section

of this report.

rfRXD0420 MAX7033 RXM-315-LC-PManufacturer Microchip Maxim LinxFrequency Range 300-450 MHz 300-450 MHz FSK/ASKPower Consumption 8.2mA 5.2mA 5mAIF Frequency 455kHz to 21.4MHz 10.7MHz Not AvailableModulation Mode ASK/FSK/FM ASK ASKPrice $2.79 $4.53 $17

Table 3.3: Receiver IC Possibilities

3.3 Repeater

All of the RKE systems that will work with the repeater are designed for a single

frequency at 315MHz, which means that in order for the car to open, a 315MHz signal

must be received and retransmitted on the same frequency.

This leads to three basic repeater designs:

1. Simultaneous Retransmission - The received signal is simultaneously

retransmitted on a separate, highly isolated antenna. This is the simplest

system, requiring essentially no control circuitry. It requires, however,

directional antennas which are highly isolated from one another if feedback is

to be avoided.


2. Waveform Storage – The incoming waveform is mixed down to a low IF and

then sampled with an A/D converter. The resulting data is stored till the end of

the transmission is detected. The waveform is then mixed back to the RF

frequency and retransmitted. This technique would retransmit ASK and FSK,

but would offer little gain advantage and frequently transmit extra noise. High

performance signal processing capability along with a large memory would be

required.

3. Demodulating the signal – The incoming signal is demodulated and stored.

After the end of the transmission is detected, the data is output to an ASK

transmitter and sent again as before. This approach is limited to ASK and

would require novel circuitry if it is to work with more than a very small

variety of automobiles. This could be implemented using either a

microcontroller or a DSP.

3.3.1 ASK Theory

Amplitude Shift Keying (ASK) is the simplest form of bandpass digital

communication. The premise is simple – a carrier at the frequency of transmission is

adjusted to different levels in order to represent different sequences of digital data.

The binary form of ASK (OOK, or on/off keying) is even simpler – the carrier is

turned on and off. When the carrier is on, a “1” is being sent. When the carrier is off, a

zero is being sent. In the example below, a simple sample sequence “1 0 1 0 1 1 0 0” is

modulated. A 2 Hz sine wave is sent. It is then multiplied by bit value being sent for each

bit in the sequence. Because the data in the example is being sent at 1 bit/s, the sinusoid is

multiplied by each bit for 1 second. In figure 3.6, an example baseband digital signal is


seen along with a carrier generated at the given frequency. By multiplying the carrier by

the baseband waveform, a bandpass digital signal is generated. [Digital Communications]

Mathematically, this can be expressed as:

(3.3.1)

0 1 2 3 4 5 6 7 8

0

0.5

1

Message m(t)

Time [s]

0 1 2 3 4 5 6 7 8-1

-0.5

0

0.5

1Carrier s(t)

Time [s]

Figure 3.6: Digital waveform (above) and carrier (below) which comprise the signal for ASK

0 1 2 3 4 5 6 7 8

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time

Mag

nitu

de

ASK Modulated Data

"1" "1""1""1""0" "0""0" "0"

Figure 3.7: Example of ASK modulation of the sequence “1 0 1 0 1 1 0 0”


Obviously the modulated signal is not band limited. Therefore, filtering is performed

before the signal is finally transmitted. This filtering leads to distortion, but at slow data

rates with relatively wide bandwidth, like those encountered in RKE systems, the effect

on communication is negligible.

Once the signal has been transmitted, it is corrupted by noise. The simplest noise

model is white, Gaussian noise.

(3.3.2)

For example:

0 1 2 3 4 5 6 7

x 10-3

-4

-3

-2

-1

0

1

2

3

4

5Noise Corrupted Signal

Time [s]

Figure 3.8: Signal Corrupted by Gaussian Noise

The signal is then filtered heavily. Finally, an envelope detector filters and rectifies

the signal:


0 1 2 3 4 5 6 7

x 10-3

-0.2

0

0.2

0.4

0.6

0.8

1

1.2Envelope Detected Signal

Time [s]

Figure 3.9: Signal after going through the envelope detector

In spite of what figure (3.9) may look like, the data can be successfully demodulated

and stored.

3.4 Transmitter

The final stage of this repeater system will have to be a transmitter. The primary

function of the transmitter is to amplify the power in the signal so that it will be able to

reach the vehicles existing antenna. There does not have to be a lot of power in the signal

being retransmitted from the repeater system to the vehicle’s receiver. This is because the

signal does not have to travel very far. The signal only has to be able to go from the

repeater system in vehicle, most likely in the back seat of the vehicle, to the receiver in


the vehicle, normally placed under the dashboard. In fact, a less powerful transmitter is

desired since it would be a smaller current draw.

There are two basic design concepts for the transmitter. It can be built using discrete

components or the transmitter can be bought from a company that manufactures RF

transmitters.

The transmitter for this project does not have to be very complicated since the total

power amplification requirements are small. Therefore, it is possible to build a transmitter

from discrete components. The basic design for a transmitter is shown below in figure 8.

Figure 3.10: Transmitter block diagram

This design includes a buffer, a power amplifier, and an oscillator. To design this

system discretely means that each one of these components would be designed separately

and then put together to make the transmitter. The design of the individual components

would most likely mean buying the components from RF manufactures. To design these

components from transistors up is beyond the scope of this project.

There are large numbers of existing RF transmitters that have been designed for

RKE systems. It would be possible for this system to take an existing transmitter,

05512 RKE Repeater

Directional coupler

Lowpass filter

Power Controller

Modulation Input

DiagnosticsForward

Reverse

32

designed for RKE systems and use as our transmitter. The only design involved would be

picking the transmitter that best fit the specifications for this project. Some the

possibilities are as follows:

Part # ADF7012 MAX1472 TH7107 rfHCS362F

Manufacture Analog Decives Maxim Melexis Microchip

Modulation Mode FSK/ASK ASK FSK/ASK ASK, FSK

Frequency Range

50-1000 MHz

300-450 MHz

315/433 MHz

310-480 MHz

Maximum Data Rate 150kbs 100kbs 40kbs 3334bps

Output Power -16dBm to +13dBm +10dBm -12dBm

to +2dBm-12dBm to

+2dBmPower

Consumption 21mA 5.3mA 4.8 to 11.5 mA

4.8 to 11.5 mA

Price: $1.89 $3.74(free Samples) $6.04 Samples

Available

Table 3.4: Transmitter IC Possibilities

3.5 Filters

One of the most important design considerations for this project is the amount of

noise interfering with the system. If large enough, this noise can completely distort the

signal and prevent the repeater from communicating the signal to the vehicle’s receiver.

To keep the noise from dominated the system analog filters must be incorporated into the

design. There are three important filters needed in the system. These are the preselector,

the intermediate frequency (IF) filter, and the transmitter output filter. These can be

implemented using active filters, passive filters, or SAW filters.

3.5.1 Preselector


The first filter needed on the receiver is called the preselector or front end filter. This

should be a bandpass filter centered at the operation frequency of the system, in this case

315MHz. The purpose of this filter is to reduce the amount of noise coming into the

system by only allowing a narrow band around the given center frequency into the

system.

The preselector must be a bandpass filter with a center frequency at 315MHz. It must

have a bandwidth of less then 600 kHz. It has to have a fairly good attenuation outside of

the bandwidth. Finally, it must match the 50Ω load on the input and a 50Ω load on the

output since the T/R switch will have 50Ω impendence and the input the receiver circuit

will be designed to have 50Ω impedance.

3.5.2 Intermediate Frequency Filter

The second filter need on the receiver is on the output of the receiver. This is should

be low pass intermediate frequency filter (IF). The purpose of this filter is to reduce

prevent the image frequencies from continuing to detection. The image frequencies are a

result of the signal being mixed down from an RF signal to an IF signal.

3.5.3 Transmitter Output Filter

The final filter required for this system is a low pass filer. This time it is on the

output of the transmitter. It is there to prevent the image frequencies from being

transmitted. The image frequencies are a result of the signal being mixed up from an IF

signal to an RF signal.

3.5.4 Filter Designs


To implement the different filters needed for this project there are several different

filter designs that can be used, the active filter, the passive filter or the SAW filter. For

each of these types of designs, there is a board range of designs for each filter

specifications.

3.5.5 Active Filters

Active filters are filters that are designed using a mathematical approximation to meet

the desired specifications. These filters then implement the approximation using

operational amplifiers, resistors, and capacitors. To implement an active filter requires

some input power to the operational amplifiers. These filters can be designed to include a

gain. Examples of some mathematical approximations for the filters are:

Butterworth Approximation: (3.5.1)

Chebyshev Approximation: (3.5.2)

For these approximations α is the attenuation in decibels at some frequency ω. The

designer uses these to find n which is the order of the filter.

3.5.6 Passive Filters

Passive filters are implemented using only resistors, capacitors, and inductors. These

are components that do not require any power to operate. These filters are designed using

the same mathematical approximations as the active filter. After these filters have been

designed as an active filter a transformation can be preformed on them to make them into


a passive filter. This is called a lossless-ladder transformation, since the combination of

passive components is called a ladder and to make it lossless is important. Some

examples for passive filter are:

C 1 2.0 0 1 5 p

C 1 3.0 0 1 5 p

1 2L 6

8 u H

1

2

L 71 6 uH

1

2

L 81 6 u H

C 1 4

. 0 3 2 p

R 1 3

5 0

R 1 45 0

V 71 V a c0 V d c

0

V

Figure 3.11: A passive bandpass filter

Passive Bandpass Filter

0

0.1

0.2

0.3

0.4

0.5

0.6

300

301

302

302

303

304

305

306

306

307

308

309

310

311

311

312

313

314

315

315

316

317

318

319

319

320

321

322

323

324

324

325

326

327

328

328

329

330

Frequency (MHz)

Mag

nitu

de (V

)

Figure 3.12: Frequency response of a passive bandpass filter


C 31 . 6 n

1 2L 2

8 uH

C 41 . 6 n

R 35 0

V 21V a c0 V d c

R 4

5 0

0

C 73 . 2 n

1 2L 4

1 6 u

C 83 . 2 n

R 75 0

V 41V a c0 V d c

R 8

5 0

0

Design for f=1MHzDesign for f=2MHz

C 1 03 . 2 n

R 115 0

V 61 V a c0 V d c

R 1 2

5 0

Single C Design for f=1MHz0

C 91 . 6 n

R 95 0

V 51 V a c0V d c

R 10

5 0

0

V

VV

V

Single C Design for f=2MHz

Figure 3.13: Some lowpass IF Filters

IF Passive LowPass Fitlers

0

0.1

0.2

0.3

0.4

0.5

0.6

10 280

550

820

1090

1360

1630

1900

2170

2440

2710

2980

3250

3520

3790

4060

4330

4600

4870

5140

5410

5680

5950

6220

6490

6760

7030

7300

7570

7840

8110

8380

8650

8920

9190

9460

9730

1000

Frequency (KHz)

Mag

nitu

de (V

)

Single C f=2Mhz Single C f=1MHz Design f=2Mhz Degisn f=1Mhz

Figure 3.14: Frequency response of various IF lowpass filters


C 1 01 0 p

1 2L 5

5 0 n H

C 1 11 0 p

R 1 15 0

V 61 V a c0 V d c

R 1 2

5 0

0

Design for f=315MHz

C 12 0 p

1 2L 1

2 0 n H

C 22 0 p

R 15 0

V 11 V a c0 V d c

R 2

5 0

0

C 38 p

1 2L 2

4 0 n H

C 48 p

R 35 0

V 21 V a c0 V d c

R 4

5 0

0

V

V

V

VV

V

C 56 p

1 2L 3

3 2 n H

C 66 p

R 55 0

V 31 V a c0 V d c

R 6

5 0

0

C 75 . 3 p

1 2L 4

2 6 . 5 n H

C 85 . 3 p

R 75 0

V 41 V a c0 V d c

R 8

5 0

0

Adapted Design for f=315MHz

Design for f=600MHz

Design for f=500MHz

Design for f=400MHz

C 91 0 . 1 p

R 95 0

V 51 V a c0 V d c

R 1 0

5 0

0

Single C Design for f=315MHz

Figure 3.15: Some Transmitter PA Low Pass Filters for different cutoff frequencies

Low Pass Filters

0

0.2

0.4

0.6

0.8

1

1.2

1 28 55 82 109

136

163

190

217

244

271

298

325

352

379

406

433

460

487

514

541

568

595

622

649

676

703

730

757

784

811

838

865

892

919

946

973

100

Frequency (MHz)

Am

plitu

de (V

) for

1V

inpu

t

Adapted Design f=315Mhz Design f=400MHz Design f=500MHzDeisgn f=600MHz Deign f=315MHz Design Single C f=315MHz

Figure 3.16: Frequency response of the transmitter low pass filters


3.5.7 SAW Filters

A surface acoustic wave (SAW) filter is a passive filter which does not use normal

discreet elements such as resistors, capacitors, or inductors. It is a thin metal film

structure deposited on top of a piezoelectric crystal substrate, definition found at

http://www3.sympatico.ca/colin.kydd.campbell/. An example of a simple SAW filter is

shown below:

Figure 3.17: SAW Filter

The filter only resonates at a specific frequency. Because it only resonates at a given

frequency, it acts as a very narrow band filter centered at that frequency. This type of

filter is advantageous because it has a very narrow pass band and does not require any

power to implement. The disadvantage is that it is expensive. To implement a SAW filter,

an impedance match must be designed. Below is an example of a SAW filter

implemented with impendence matching to 50 Ohm:


http://www3.sympatico.ca/colin.kydd.campbell/

Figure 3.18: SAW Filter Impedance Matching

3.6 System Control

There are several important functions that require control circuitry. These include

enabling the transmitter and receiver and controlling the T/R switch. A microcontroller is

required to perform these operations. The microcontroller will also need to store the

signal received. The controller must operate fast enough to decode the signal, have

sufficient memory to store the decoded data, and have enough outputs to control all of the

other circuitry.

The microcontroller will control the enable for the transmitter; the transmitter

only needs to be on when the signal is transmitting so that power is not wasted. It also

controls the enable for the receiver. The receiver will only turn off when the transmitter is

transmitting; this will increase the isolation and prevent feedback. The microcontroller

will control the T/R switch. The switch needs to be set to receiver when the receiver is

enabled and set to the transmitter when the transmitter is enabled. Finally, it will send the

stored data to the transmitter during retransmission.

The microcontroller needs to operate fast enough to decode the input data. If the

data rate is too fast for the microcontroller then it will store an incorrect signal and

repeater will not function. It also needs to have a stable time reference. This time


reference will most likely be set by an external crystal - if the time base varies then the

microcontroller’s internal clock will be disrupted, preventing a successful storing and

retransmission of the signal.

3.7 Housing

The housing will be as small and attractive as possible. It should not occupy any

excess space and should be able to be attached to the parts of the car as appropriate.

Further development of the housing solution cannot be completed until the antenna and

circuit board have been completed.


4. Feasibility Assessment

4.1 Antenna

The size and housing unit of this project limits the length of the antenna design. Since

space does not permit for a non-wire antenna, the quarter-wave antenna was the most

feasible for this project because of its length. Since the user should be able to use the key

fob from all directions it is required that the antenna be omni directional as opposed to

directional antenna. Using the weighted method of feasibility the quarter-wave antenna

was the most feasible. The quarter wave antenna is also an optimum length because the

gain diminishes with a decrease in antenna length.

Evaluate each additional concept against the baseline, score each attribute as: 1 = much worse than baseline

concept 2 = worse than baseline 3 = same as baseline 4 = better than baseline 5= much better than baseline

Hal

f-w

ave

Ant

enna

Hal

f-w

ave

Ant

enna

Qua

rter-

Wav

e A

nten

naQ

uarte

r-W

ave

Ant

enna

Loop

Ant

enna

Loop

Ant

enna

Rel

ativ

e W

eigh

tR

elat

ive

Wei

ght

Sufficient Student Skills?Sufficient Student Skills? 5 5 5 11%

Sufficient Lab Analysis Equipment?Sufficient Lab Analysis Equipment? 4 4 4 11%

Cost of Materials?Cost of Materials? 5 5 5 3%

Cost of Purchased Components?Cost of Purchased Components? 5 5 5 6%

Complete within 2 quarters?Complete within 2 quarters? 4 4 4 11%

Complete by 1 student?Complete by 1 student? 5 5 5 17%

Has a similar technology been used before?Has a similar technology been used before? 5 5 5 0%

Is it theoretically possible?Is it theoretically possible? 4 4 4 19%

Size?Size? 3 5 4 22%

0%

Weighted ScoreWeighted Score 4.1 4.6 4.4

Normalized ScoreNormalized Score 90.3% 100.0% 95.2%

Table 4.1: Weighted antenna feasibility analysis

4.2 Receiver


An estimation of the required gains, losses, and intercept points must be calculated in

order to show the feasibility of the system. In general, the RF amplifier gain should not

exceed 20 dB as it would create many problems. These issues include unavailability of a

single device, instability of the system and the unachievable required amplifier intercept

point. A filter insertion loss of 3 dB or less could also be implemented without any

problems.

The selection of IF frequency is also a very crucial process because it would

determine the location of the image and the half IF spurious response frequencies. The

choice of IF frequency, however, is not totally flexible as crystals and IF filters are only

manufactured in certain standard center frequencies. The IF frequency must also be

different from harmonics of the other discrete frequencies such as the digital clock

operating frequency and reference frequency.

When selecting the first LO injection side, a few considerations must be thought of.

High-order spurious responses and self-quieting frequencies may favor on or the other

injection side, once the IF frequency has been chosen. Also, higher-frequency oscillators

typically have worse SSB phase noise but the required voltage controlled oscillator

(VCO) tuning range (in percent) for synthesized sources is less for high-side injection

than for low-side injection. The chosen mixer may have a limited frequency of operation,

forcing low-side injection. A lower-frequency LO that is multiplied up in frequency may

sometimes offer advantages over a high-frequency LO without frequency multiplication

as well.

There are a few differences between passive and active mixers. It is one of the most

important selection that would significantly affect the receiver overall performance.


While passive mixers possess better IM performance, it requires much higher local

oscillator power and do not provide conversion gain. Active mixers are directly opposite.

Active mixers require less local oscillator power and still do not have a much better noise

figure. The second-order intercept point of the mixer will determine the necessity of the

RF filtering for the half IF spurious response. Also, with higher amplification of the VCO

signal, the wide band noise will be higher. As a result, an injection filter may be needed

in order to suppress image noise to achieve better sensitivity. This particular filter does

not necessary have to be highly complicated. A simple low-pass filter would be adequate

to suppress the second harmonic from the LO signal and help balancing the mixer by

improving the mixer second intercept point.

The LO technology selection is probably one of the most flexible part of the receiver

which relies heavily on the receiver application. For a single-frequency receiver, such as

this project, a simply crystal oscillator can be used. Although in many other systems, a

frequency synthesizer or a LC discrete inductor-capacitor oscillator circuit could be

possible candidates.

The RF filter must be chosen to correspond with the determined IF frequency and the

first LO injection side. Then, a filter topology that rejects the appropriate signal must be

selected. For this specific application, a high-side injection must be used in order to reject

the high-frequency noise that is coupled with the signal. Since the selectivity is a trade off

for insertion loss, the selected filter’s selectivity must be sacrificed as the input to the RF

amplifier must have low insertion loss.


The RF amplifier is the last block of the receiver circuitry. It is there to fine-tuned the

signal properties after all of the other earlier mentioned parts are determined. It is much

more feasible to shape the signal in this stage than in other stages.

As this particular receiver design is aimed to have low power consumption, there are

more constraints on its operation. With high tendency of the receiver to overload and a

possibility of IM distortion, it is critical to design the receiver to have as narrowband as

possible. This type of receiver usually alternately switches itself on and off to conserve

battery power. [RF Design Guides]

When the feasibility assessment was carried out to compare the benefits between

receiver construction from discrete components and existing receiver IC, it would be cost

and time effective to purchase the IC. Moreover, all of the necessary components of a

receiver could be found in existing receiver IC. In the final design, rfRXD0420 will be

used. This IC will results in a receiver system that will match the need of this project at a

reasonable price. However, this existing receiver IC does not include the filters that are

necessary. As a result, additional discrete SAW and low pass filters must be purchased.

Information on filters could be found in the filter section of this report.


Evaluate each additional concept against the baseline, score each attribute as: 1 = much worse than baseline concept 2 = worse than

baseline 3 = same as baseline 4 = better than baseline 5= much better than baseline

Dis

cret

e Pa

rtsD

iscr

ete

Parts

Exis

ting

Parts

Exis

ting

Parts

Rel

ativ

e W

eigh

tR

elat

ive

Wei

ght

Sufficient Student Skills?Sufficient Student Skills? 4 4 11%

Sufficient Lab Analysis Equipment?Sufficient Lab Analysis Equipment? 4 4 3%

Cost of Materials?Cost of Materials? 2 4 6%

Cost of Purchased Components?Cost of Purchased Components? 2 4 8%

Complete within 2 quarters?Complete within 2 quarters? 3 4 14%

Complete by a student?Complete by a student? 3 4 17%

Has a similar technology been used before?Has a similar technology been used before? 4 5 0%

Is it theoretically possible?Is it theoretically possible? 4 5 19%

Does it use the spectrum well?Does it use the spectrum well? 4 5 22%

0%

Weighted ScoreWeighted Score 3.4 4.4

Normalized ScoreNormalized Score 77.4% 100.0%

Table 4.2: Feasibility analysis of the receiver

4.3 Repeater

Three approaches for repeater design were identified. Simultaneous retransmission

was almost immediately ruled out due to the omnidirectional antenna requirement.

Because of it, the isolation between the transmit and receive antennas would be minimal

– the gain would be far greater than the isolation. This would create feedback, making the

system useless.

The IF waveform storage approach was initially the most promising. It appeared

relatively easy to implement while being extremely robust (independent of modulation

type). However, many problems existed. First, the key fobs do not have a particularly

stable frequency source. Thus, the bandwidth which would need to be stored would be

very large, requiring an extremely high performance A/D converter. The circuitry


required to implement such a device would consume a large amount of power.

Furthermore, since no form of data detection is implemented, the repeater would be

repeating noise frequently, which would be an irresponsible use of the spectrum.

Demodulating the data was the most restrictive method investigated but also the most

feasible. It limits the scope to only ASK type transmitters. It has the advantage of

requiring much lower performance parts than the IF approach as well as the ability to

detect if real data is being received. A microcontroller was decided upon over a DSP for

this approach because of power considerations. The weighted analysis agreed well with

the reasoning, as seen below:

Evaluate each additional concept against the baseline, score each attribute as: 1 = much worse than baseline concept 2 = worse than baseline 3 = same as baseline 4 = better than

baseline 5= much better than baseline Sam

ple

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Sufficient Student Skills?Sufficient Student Skills? 3 3 3 3 2%

Sufficient Lab Analysis Equipment?Sufficient Lab Analysis Equipment? 3 2 2 1 2%

Cost of Materials?Cost of Materials? 4 3 1 4 22%

Cost of Purchased Components?Cost of Purchased Components? 4 3 1 4 22%

Complete within 2 quarters?Complete within 2 quarters? 4 3 3 4 2%

Complete by a student?Complete by a student? 3 3 3 3 2%

Has a similar technology been used before?Has a similar technology been used before? 3 3 3 3 2%

Is it theoretically possible?Is it theoretically possible? 2 4 4 1 22%

Power ConsumptionPower Consumption 3 4 1 3 22%

Does it use the spectrum well?Does it use the spectrum well? 3 4 4 3 2%

Weighted ScoreWeighted Score 3.2 3.4 1.9 3.0


Normalized ScoreNormalized Score 94.2% 100.0% 55.2% 86.6%

Table 4.3: Feasibility assessment for the repeater

4.4 Transmitter

There were two basic ideas for transmitter design presented in section 3.4. These

were to either design a transmitter from discrete components or to buy a transmitter chip

that has been designed for RKE systems. Both of these ideas are feasible from a technical

point of view. To design the transmitter discretely would simply require finding the

correct parts and making sure that they operated together properly to get the desired

output. To buy a transmitter chip would only require finding the chip that best suited the

desired output.

There are two key factors for feasibility other then the technical factor. These are the

price of the design and the power consumption of the design. To design the transmitter

from discrete parts would cost more. To get a good power amplifier cost almost as much

as the entire transmitter chip. The mixer and the demodulator will also add to the cost.

The cost of the discrete parts is going to be significantly greater, therefore, than the cost

of the transmitter chip. The power consumption for the discrete parts may or may not be

less then the transmitter chip. That depends on which chip is used and what parts are used

for the discrete design. To get less power consumption in the discrete parts will drive up

the cost for the discrete parts.

Building the transmitter out of discrete parts will result in a better transmitter since

each of the parts can be higher quality. However, it will cost more and may have higher

power consumption. Since the transmitter for this project does not have to be very good,


but it does have to be cheap and low in power, the transmitter chip idea is more feasibly

to the design.


Evaluate each additional concept against the baseline, score each attribute as: 1 = much worse than baseline concept 2 = worse than baseline 3 = same as baseline 4 = better than

baseline 5= much better than baseline

Dis

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Com

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Tran

smitt

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ansm

itter

Rel

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ght

Sufficient Student Skills?Sufficient Student Skills? 4 4 11%

Sufficient Lab Analysis Equipment?Sufficient Lab Analysis Equipment? 4 4 3%

Cost of Materials?Cost of Materials? 2 4 6%

Cost of Purchased Components?Cost of Purchased Components? 2 4 8%

Complete within 2 quarters?Complete within 2 quarters? 3 3 14%

Complete by a student?Complete by a student? 3 4 17%

Has a similar technology been used before?Has a similar technology been used before? 4 5 0%

Is it theoretically possible?Is it theoretically possible? 4 5 19%

Power ConsumptionPower Consumption 1 5 22%

Does it use the spectrum well?Does it use the spectrum well? 4 5 22%

Weighted ScoreWeighted Score 3.6 5.4 0.0

Normalized ScoreNormalized Score 67.6% 100.0% #

Table 4.4: Feasibility assessment for the Transmitter

4.5 Filters

4.5.1 Preselector

There are three different design concepts for the preselector. These are an active

filter, a passive filter, or a SAW filter, as discussed in section 3.5. The key factors in the


feasibility for the preselector are the pass band, the cost of the filter, the physical

capability to implement the filter, and the power consumption of the filter. Due to the

fact that power consumption is such a big concern for this project the active filter is ruled

out.

For the preselector a passive filter will be very hard to actually implement. This is

because at it will be very hard to get the desired bandwidth it passive components. The

problem with bandwidth of the filter is that it relies completely on the load. The load for

this circuit is very small, only 50 Ω. This makes the values of the inductor and capacitors

very small and therefore more expensive and less reliable. SAW filters give amazingly

good response with very little loss and no input power. The bandwidth for SAW filter is

very narrow and therefore meets a key specification for the preselector.

Overall the SAW filter is best option for the preselector. This is because it is easy

to implement, does not require any input power and has a very narrow bandwidth.


There are only two different design concepts for the IF filter. The SAW filter can

not be used for the IF filter since this filter should be a lowpass filter rather then a

bandpass filter. Therefore, the two design concepts are either using a passive filter or an

active filter. The active filter is much easier to design and would give a gain rather then a

loss. However, the active filter is going consume power and since power consumption is

an important design consideration, passive filters will better meet the design

specifications for this project.

Figure (3.13) displays all of the different passive filter designs that were

considered for this project. Figure (3.14) shows the result from the simulation of these


different filters. The simulation in this case is an important deciding factor. For the low

pass filter there is a significantly better response due to the addition of an inductor and

capacitor. The single capacitor filter has a much slower fall time. Therefore the two

capacitor and inductor filter will be used for this project

Due to power considerations a passive filter will be used to the IF filter. To get a

sharper cut off in the filter a second order, two capacitor and inductor, filter will be used.


There are only two different design concepts for the transmitter output filter. The

SAW filter cannot be used for this filter since this filter should be a lowpass filter rather

then a bandpass filter. Therefore, the two design concepts are either using a passive filter

or an active filter. The active filter is much easier to design and would give a gain rather

then a loss. However, the active filter is going consume power and since power

consumption is an important design consideration, passive filters will better meet the

design specifications for this project.

Figure (3.15) in displays all of the different passive filter designs that were considered

for this project. Figure (3.16) in the same section shows the result from the simulation of

these different filters. The simulation in this case is an important deciding factor. For the

low pass filter there is a significantly better response due to the addition of an inductor

and capacitor. The single capacitor filter has a much slower fall time. Therefore the

second order, two capacitor and inductor, filter will be used for this project. There are

different designs for the second order filter. Each of these designs is based upon a

different cutoff frequency. For this project the magnitude at 315 MHz should be large and

then cutoff sharp after that. The modified 315 MHz design therefore works best. This


design is based upon a Butterworth approximation that was modified in the simulation to

move the frequency slightly.

Due to power considerations a passive filter will be used to the transmitter output

filter. To get a sharper cut off in the filter a second order, two capacitor and inductor,

filter will be used. To get a good response at 315 MHz and a good attenuation after that

the modified 315 MHz filter will be used.

4.5 Controller

There are a numerous controllers from various companies capable of handing the

processing necessary for the repeater. The specifications will be determined by the rest of

the system. After that, it is merely a matter of choosing an appropriate microcontroller

that has low current consumption and meets the other design needs.

4.6 Repeater Housing

Commercial viability considerations dominate the feasibility analysis of the RKE

repeater. Optimal performance might well be achieved by placing a large antenna array

on the top of the car. This, however, would lead to increased price, system complexity,

and most importantly to the end-user, an unsightly mess on the top of the car.

Placing the antenna on top of the car would lead to optimal system performance. With

the antenna mounted in such a location, it would be free from the reflections and

diffraction that it will likely experience if placed inside of the car. This, however, would

lead to a significantly more complicated housing design, as it would have to withstand

the harsh environment outside of a car (including high winds, water, temperature

extremes, collisions with bugs and other debris, and a variety of other events). The car


top location of the antenna would likely be considered unsightly by most consumers as it

would need to be placed on the roof of the car and would likely not match the paint color

of the car or the styling of the car. Additionally, some method of affixing the device to

the top of the car would be required (for example, permanent magnets). These would

likely add to the cost of the device and make installation more cumbersome, particularly

for short consumers or people with vans or sport utility vehicles.

Making the antenna a permanent part of the unit and then placing the unit in a

specified portion of the car would seem to be the most commercially viable option. As

long as the repeater is sufficiently small, the final assembly could be quite unobtrusive. It

could be little more than a small box strategically placed in the car that user does not see

or think about except to change batteries every so often.


5. Analysis and Design

From a system overview perspective, one of the most important considerations is

power consumption. Since the device should have a long lifetime on only a couple of

batteries, careful attention is paid to power consumption. Based on the design presented,

the following power budget is calculated:

Component Description Power On Current Standby CurrentSources: AA Bateries Energizer AA Bateries1 2850 mAH

Sinks: rfRXD042 Microchip 8.2mA <100nA MAX1472 MAXIMIC 5.3mA <350nA PIC16F87 Microchip 150uA <100nA T/R Switch Analog Devices <1uA

Max Current 8.351mAMax Standby 8.201mATransmitting 5.45mA

Table 5.1: Estimated power draw for circuitry1Based on two AA Energizer batteries, http://data.energizer.com/PDFs/e91.pdf

Also important in any communications system is the link budget. After analyzing the

system, the following budget was tabulated:


http://data.energizer.com/PDFs/e91.pdf

Component Value Power

1. Transmitter Power (dBW) 1mW -60.0

2. Circuit Loss (dB) 0

3. Transmit Antenna Gain 0

4. Terminal EIRP [-60.0]

5. Path Loss <65.93>

6. Other TX losses <10>

7. Received Isotropic Power [-134.978]

8. Receive Antenna Gain 5.15

9. Receive Signal Power [-131.978]

10. Noise Spectral Density <192.5>

11. Received Pr/No (dB/Hz) [62.672]

12. Data rate (dB-bit/s) (40kb/s) 46

13. Received Eb/No (dB) [16.651]

14. Implementation loss (dB) <1.5>

15. Required Eb/No (dB) <10.0>

16. Margin (dB) [[5.15]]

Table 5.2: Link Budget Analysis

5.1 Antenna Design

Based on the analysis seen in previous sections and the following information on the antenna:

An quarter wave antenna with the length adjusted to 0.226m for optimal gain and

impedance. A solid AG wire of size 18 and a wire diameter .0403in would be used for the

quarter-wave antenna attached to a BNC connector. The following are the characteristics

for the antenna:


Figure 5.1: Directive Gain pattern of the Quarter wave antenna

Figure 5.2: Current distribution of the quarter wave antenna


Freq(MHz)

Resistance()

Reactance()

Impedance()

Phase(Deg)

VSWRdB

S11dB

S12dB

315 35.789 -.79302 35.798 -1.27 1.3978 -15.603 -1.5756

Table 5.3: Electrical characteristics for a quarter wave antenna

The final antenna design is seen in the following figure:

Figure 5.3: The final antenna design

5.2 Receiver Design

The final receiver prototype would be implemented by a combination of filters

and the existing rfRXD0420 receiver IC.


Figure 5.4: rfRD0420 Pin Diagram

5.2.1 Bias Circuitry and Frequency Synthesizer

In this particular chip, the receiver enable input (ENRX) is located at pin 28. It has

the ability to pull down to Vss. This is crucial to the bias circuitry which provides the

bandgap biasing and shutdown capabilities. Pin 26 is used in order to provide the

reference frequency to the PLL using a crystal locator. An external loop filter is

connected to pin 29 to control the dynamic behavior of the PLL.

5.2.2 Low Noise Amplifier

The input to the Low Noise Amplifier (LNA) is connected to pin 31, which then

produces an output at pin 3. The mode of the LNA is controlled by connecting different

voltages to pin 2. The built-in LNA has the capability to be in either high gain or low

gain mode.

5.2.3 Mixer and IF Preamp


After the signal is amplified, the signal is then passed through 1IFIN pin (pin 4) in

order to step down the signal to the Intermediate Frequency (IF). The mixer is biased

through pins 6 and 7. These inputs would keep the mixer balanced. The 1IFOUT (pin 9) has

an impedance of 330 ohms in order to perfectly match with the cost effective ceramic IF

Filters.

5.2.4 IF Limiting Amplifier with RSSI

IF Limiting Amplifier stabilizes the signal after it passes through the IF Preamp to

prepare it for demodulation. The signal input is fed into 2IFIN (Pin 11). At the same time

Pin 21 also generates the Received Signal Strength Indicator (RSSI). In this stage, a 390

ohm resistor is placed paralleled to the 2IFIN pin in order to match the output impedance

of 330 ohm ceramic IF filters.

Due to the fact that this project deals with amplitude shift keying (ASK), RSSI is

compared to a reference voltage. The output of this pin has an internal resistance of 36k

ohms which converts the RSSI current to voltage. [Microchip Specification Sheet]

The following figure is the complete receiver schematic, including the filters:


Figure 5.5: Full Receiver Schematic


5.3 Transmitter

The final transmitter design will be based around the MAXIM/IC MAX1472 ASK

transmitter. The transmitter has a sufficiently high data rate, desired low output power,

and very low power consumption. It requires minimal external circuit that lends easily to

integrate with the remainder of the circuit.

Figure 5.6: Transmitter Schematic

The only additional circuitry required will be a crystal which controls the frequency

for the output of the transmitter and a filter. The filter shown here is a low pass filter and

the values are discussed in the filter section of the report, section 3.5.3. The other added

circuitry is for power adjustment. This output circuit is simulated and is shown below in

figure 5.7.


C 12 0 p

C 22 0 p

C 36 8 0 p

C 42 2 0 p

1 2L 1

2 0 n H

1

2

L 21 0 u H

R 25 0

R 3

5 0

V 23 V d c

0

0

0

V 3

F R E Q = 3 1 5 0 0 0 0 0 0V A M P L = 1V O F F = 0

V

R 4

Figure 5.7: Transmitter Output Circuitry

Simulation From Output Circuitry

-0.5

0

0.5

1

1.5

2

2.5

3

0

0.063

4928

1.301

6163

3.285

7991

5.269

9818

7.254

1646

9.238

3473

11.22

253

13.20

6713

15.19

0896

17.17

5078

19.15

9261

21.14

3444

23.12

7627

25.11

1809

27.09

5992

29.08

0175

31.06

4358

33.04

854

35.03

2723

37.01

6906

39.00

1088

40.98

5271

42.96

9454

44.95

3637

46.93

7819

48.92

2002

Time (ns)

Mag

nitu

de (V

)

10 Ohms 100 Ohms 1k Ohms

Figure 5.8: Simulation of Transmitter Output Circuitry

This chart shows the results from the simulation for the transmitter circuitry. The two

50Ω resistors simulate the output impedance from the transmitter chip and input

impendence to the antenna. The other resistor is a variable resistor. This resistor controls

the power amplification to the signal. The result of changing this resistor is shown above


in figure 20. The smaller the resistor the higher the gain in the system is going to be. This

was simulated with a 315 MHz signal so the filter will not affect this simulation. The

simulation for the filter part of this circuit is shown below in section 5.4.3.

The transmitter chip used in this design is MAX1472. This is a low power, 300 to 450

MHz transmitter that has been designed for RKE systems. This transmitter includes a

phase lock loop that is controlled by an external crystal. The input signal, data-in signal,

and an enable signal are sent through an ADD gate. This means that the data-in is only

amplified if the enable is high. The transmitter also includes a power amplifier. The level

that the power is amplified by is set by an external circuit. That external circuit includes a

low pass filter and control circuitry for the power amplifier. The circuitry draws the

power amplifier to a certain level. The resistor R1 seen in figure (5.7) controls the level

of the amplifier. In figure (5.7) R1 is set to 270Ω which makes the transmitter amplify the

signal by approximately 10dBm.

In the transmitter, MAX1472, pin 1 is called XTA1 and connects the chips

internal oscillator to the external crystal. Pin 8 is called XTA2 and it connects the internal

oscillator to the other side of the crystal. Pin 2 is called GND and it connects the chips

internal ground to the external ground. Pin 7 is called VDD and it provides the power to

the chip. In figure 19 is connected to a capacitor which projects the chip and to power.

The power into this chip can vary from 2.1 to 3.6 VDC and the current in is normally

5.3mA and a maximum input current of 16.4mA. Pin 3 is called PAGND is the power

amplifier ground; it is connected to the same ground as pin 2. Pin 4 is called PAOUT it is

the output from the power amplifier and it is the output from the transmitter. Pin 5 is

called ENABLE and it is turns on the chip. Enable is connected to the microcontroller; if


low the transmitter sleeps and draws very little current, when high the transmitter accepts

the input signal and amplifies it. Pin 6 is called DATA and it is the input to the

transmitter. This is all shown on table (5.2).

Pin LABLE Description 1 XTA1 Connected to external Crystal2 GND Connected to external ground3 PAGND Connected to external ground4 PAOUT Transmitter Output5 ENABLE Microcontroller control6 DATA Transmitter input7 VDD Connected to external power8 XTA2 Connected to external Crystal

Table 5.2: MAX1472 Pin Description

To actual simulate the transmitter is not possible, the only way to know for certain

that this transmitter will work it to buy it and test it. However, we are confident that this

transmitter will work well in this system because it has the gain that is required and the

rest of the transmitter is fairly simple.


Figure 5.9: Complete Transmitter Schematic


5.4 Filters

5.4.1 Preselector

It was decided that the best preselector filter to use was a SAW filter. This means that

design for this filter involved finding a SAW filter that meets the needs of this project.

The SAW filter needs to have a wide enough bandwidth to ensure that any small variance

in the frequency is included. To do this bandwidth needs to be at least 600 kHz with a

center frequency of 315 MHz. The SAW filter needs to be a passive SAW filter. It needs

to have a small insertion loss.

SAW filters can not be easily designed and manufactured given the tools that students

have, therefore it has to be bought. The SAW filter that was finally settled on is the

162988 produced by COM DEV SAW Products. This filter has a pass band of 830 kHz, a

center frequency of 315 MHz, and an insertion loss of 2.5dB. This is the filter:

Figure 5.10: SAW Filter

The frequency response for this filter could not be simulated using Pspice since there

is no working SAW component in Pspice. Therefore, the frequency response for this

filter is taken from the data sheet and are shown below in figure (5.11).


Figure 5.11: SAW Filter Frequency Response


It was decided that the best low pass filter to use for the intermediate frequency was a

second order passive filter. This filter’s cutoff frequency was designed for 1MHz since

anything more than that is not necessary. The receiver should be able to bring down the

final input signal to below 1MHz and therefore, this filter will attenuate the noise in

higher frequencies and pass the mixed down signal to the microcontroller stage of the

repeater. The design for the second order 1MHz low pass filter is shown below in figure

(5.12) and the results from the simulation are also shown below in figure (5.13).

C 73 . 2 n

1 2L 4

1 6 u

C 83 . 2 n

R 75 0

V 41 V a c0 V d c

R 8

5 0

0

Design for Intermediate Frequency Low Pass Filter

V

Figure 5.12: Intermediate Frequency Low Pass Filter


Intermidate Frequency Low Pass Filter

0

0.1

0.2

0.3

0.4

0.5

0.6

0

0.16

0.32

0.49

0.65

0.81

0.97

1.14 1.

3

1.46

1.62

1.78

1.95

2.11

2.27

2.43

2.59

2.76

2.92

3.08

3.24

3.41

3.57

3.73

3.89

4.05

4.22

4.38

4.54 4.

7

4.86

5.03

5.19

5.35

5.51

5.68

5.84 6

Frequency (MHz)

Mag

nitu

de (V

)

Figure 5.13: IF Filter Frequency Response


The transmitter output circuitry is shown above in figure (5.7). Part of this

circuitry is a second order low pass filter. The design for this filter was done using

315MHz as the cutoff frequency and then modifying the design to shift the frequency in

such a way that 315MHz was passed at full strength. The final design for the filter is

shown below in figure (5.14). The results for the simulation of this filter are shown below

in figure (5.15).

C 72 0 p

1 2L 4

2 0 n

C 82 0 p

R 75 0

V 41 V a c0 V d c

R 8

5 0

0

Design for Transmitter Output Filter

V

Figure 5.14: Transmitter Output Filter


Transmitter Output Filter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.1

0.13

0.17

0.21

0.28

0.35

0.46

0.59

0.76

0.98

1.26

1.62

2.09

2.69

3.47

4.47

5.75

7.41

9.55

12.3

15.8

20.4

26.3

33.9

43.7

56.2

72.4

93.3

120

155

200

257

331

427

550

708

912

Frequency (10MHz)

Mag

nitu

de (V

)

Figure 5.15: Transmitter Filter Frequency Response

5.5 T/R switch

Due the fact that only one antenna is used for this design a transmitter/receiver

switch is needed in front of the repeater to indicate the path the signal needs to take. This

switch needs to have good isolation to keep the signal from crossing over into the other

side of the system. To keep the design cheap and at the same time keep the isolation good

a switch from Analog Devices is going to be used. This switch, ADG901, has an isolation

of 43 dB and has a very low power consumption of less then 1μA. The switch is shown

below in figure (5.16).


Figure 5.16: Transmitter/Receiver Switch

This chip is controlled by the microcontroller. If the control signal into pin 2 is

low then a path between the antenna and the receiver is established. If the control signal

into pin 2 is high then a path between the antenna and the transmitter is established. The

pins configuration is described in table (5.3).

PIN LABLE Description1 VDD Connected to external power2 CTL Microcontroller control3 GND Connected to external ground4 RFC Connected to Antenna5 RF2 Connected to Receiver6 GND Connected to external ground7 GND Connected to external ground8 RF1 Connected to Transmission

Table 5.4: ADG918 Pin Description

5.6 Housing Design

The housing will be the minimum size necessary to contain the entire unit, including

the antenna and the batteries. The housing will be constructed from a durable material

capable of withstanding the temperature extremes that could be encountered in an


automobile as well as long term exposure to sunlight. It will be a neutral color. The final

housing will fit well in a wide variety of vehicles.

The antenna size is the primary consideration in trying to make sure the unit is not

cumbersome. Because a ¼ antenna is desired, a helical or folded dipole configuration will

likely be implemented in order to conserve space.

A prototype housing design is presented below. The final design may have to be

modified to take into account the repeaters final placement in the car. The housing will be

different if, for instance, it is found that the performance is better when attached to the

rear window versus resting behind the rear seat.


Figure 5.17: Specifications for the housing


Final dimensions for the housing will be determined after a working prototype of the

repeater has been produced. Then it will be possible to optimize the board layout in order

to minimize housing size and maximize antenna effectiveness.

Placement of the housing in the automobile will be determined upon completion of a

working prototype. The unit will be placed in various locations in a number of different

common automobiles. The automobiles will be placed in a controlled environment. The

repeater will then be tested in each automobile from a variety of different angles and

distances. At each location the different key fob functions will be transmitted and the

ability of the repeater to cause the automobile to operate as desired will be noted. The

repeater will be moved to different locations in the vehicle and the affect on performance

will be noted. In this way, a list of proffered locations for the repeater will be empirically

formed. The complex environment of a parking lot and the interior of the car are too

complicated to allow for an adequate model to be formed.

5.7 Control System Design

The controller selected is the Microchip PIC16F737. It is a 28 pin device capable of

operating at speeds between DC and 20 MHz, containing 368 bytes of RAM. The

pertinent features along with reasoning behind their selection are below:

Feature ImportanceInternal Oscillator

Accurate internal oscillator eliminates need for external clock

Analog Comparators

Needed for dynamic detection of received signal if receiver comparator is not used.

Number of digital outputs

Many of the pins are assigned multiple functions. Other similar devices with lower pin-counts lacked a sufficient


number of outputs to control all of the other devices.Memory With 368 bytes of RAM available, external memory is

not necessary, simplifying design and ensuring faster access time.

Speed With operation up to 20 MHz, having enough time to perform operations between detections is not a problem.

Cost At such a low cost the device offers an affordable solution.

Table 5.5: Control System Specs [Microchip]

Since each byte of memory will contain the number of ones or zeros encountered in a

row from the receiver, the will account for a total of up to 368 byes of received data from

the key fob. This is far larger than any known RKE system encountered up to this point

and should allow for some margin of error on the part of the receiver. Because the

PIC16F87 is based on true Harvard architecture, reading and writing to its internal

memory takes only one cycle, eliminating the timing concerns that other approaches may

have required.

The controller must control the state of the T/R switch (connected to the transmitter

or receiver), the receiver enable, and the transmitter enable. It must also store the detected

data from the receiver and send it to the transmitter. The following connections are

necessary for the microcontroller:

Connection TypeRX ENABLE OUTPUTTX ENBALE OUTPUTT/R SWITCH OUTPUTDATA OUT OUTPUT

RX DATA IN INPUT

Table 5.6: Connections Needed for Microcontroller


Name Pin Use Connection DescriptionRA2/AN2/Cvref/Vref 1 RA2 TX ENABLE Held high for transmission

RA3/AN3/Vref+/C1OUT 2 RA3 TX DATAASK Data sent by transmitter. High keys transmitter

RA4/AN4/T0CK1/C2OUT 3 *RA5/MCLR/Vpp 4 *Vss 5 Vss VssRB0/INT/CCP1 6 *RB1/SDI/SDA 7 *RB2/SDO/RX/DT 8 *RB3/PGM/CCP1 9 *RB4/SCK/SCL 10 RB4 RX DATA IN Data sent to MCU from receiverRB5/SS/TX/CK 11 *RB6/AN5/PGC/T1OSO/T1CKI 12 *RB7/AN6/PGD/T1OSI 13 *Vdd 14 Vdd VddRA6/OSC2/CLKO 15 *RA7/OSC1/CLKI 16 *

RA0/AN0 17 RA0 TR SWITCHHeld low for antenna connected to RX, high for TX

RA1/AN1 18 RA1 RX ENABLEHold high to enable receiver, always except when TX is on

*Pins not connected. If alternate architecture is necessary, pins may be used.

Table 5.7: Pin connections to the Microcontroller [Microchip]


Figure 5.18: PIC16F87 Microcontroller Schematic Diagram

Below is an overview of the control process:


Figure 5.19: High Level Overview of Control Systems

The controller rests in a low power state while the transmitter is powered off and the

antenna is connected to the receiver. Once a “1” is detected from the receiver, the

controller starts recording data bits and storing them to memory. This continues until a

sequence of zeros is detected. The receiver is then turned off, the antenna is switched to

the transmitter, and the transmitter is turned on. The transmitter transmits the data, and is

then turned off. The antenna is switched back to the receiver, which is then powered on

again and the system reverts to the listening state.


When the repeater is powered on, it should default to a low power state where the

receiver is monitoring incoming signals. The PIC has a default power on state, and so

each of the output pins must be set corresponding to its function. The following settings

are necessary at power on:

Pin Type OutputRA0 OUTPUT 0RA1 OUTPUT 1RA2 OUTPUT 0RA3 OUTPUT 0RA4 - -RA5 - -RA6 - -RA7 - -RB0 - -RB1 - -RB2 - -RB3 - -RB4 INPUT -RB5 - -RB6 - -RB7 - -

Table 5.8: Pin States at power on

Seen below is the power on coding sequence. It sets the appropriate pins as input or

outputs, then sets the received signal change as an interrupt. After everything is set, the

receiver is turned on and the signal is listened for.


Figure 5.20: Power On Sequence

Once the PIC16F87 is in idle mode, it will draw very little current until it is

interrupted by a change in the value on the RB4 (Receiver data) pin. During this time, the

antenna is held by the receiver and the receiver continuously receives data.

When the receiver detects a one, the value of pin RB4 changes. This calls the

microcontroller interrupt, which executes the code at address 0x04. At this location a

subroutine will be called in order to input data that is being received. The routine will

sample the detector output at a rate of 40,000 samples/s. The subroutine, as seen below,


will indicate the reception of a 1 by putting 1 in the first memory location through setting

the indirect register.

Figure 5.21: Interrupt handling for change on RB4

Once the interrupt has been executed, the reception begins. A RAM location name

stream stores the last detected bit, be it a “1” or a “zero”. As reception progresses, the

stream of incoming data is rotated through “STREAM”. The data that is rotated out has

already been accounted for in the counter RAM locations. It is only held in STREAM so

that the binary filtering operation can be performed on the data.


The first order of business is to make sure that actual data is being received and it was

just not some random noise. This will ensure that random transmissions are infrequent.

Four bits are read, spaced by 1/40000 s. These bits are each rotated into STREAM. If

there is only one high bit in stream, actual data is not being transmitted, so the receive is

canceled and the system returns to a listening state. If valid data is detected, the receiver

enters the receiver loop.


Figure 5.22: Routine to check for valid received data and enter receive mode.


The receive loop checks pin RB4 (output of the receiver) and records its state. This

state is rotated into the STREAM memory. Using indirect addressing, the RAM positions

are cycled through. Because the data is being detected at a very high rate, a number of 1’s

and 0’s will be detected in a row every time will be quite high. This makes memory

allocation most efficient by recording the number of 1’s and zero’s detected from the

receiver in a row. An example is seen below:


Figure 5.23: Rate independent detection of the ASK signal

As long as the data is retransmitted at the same rate it is collected at, a nearly identical

signal to the one received will be transmitted.


The bit that has just been detected is not the one, however, that is transferred to the

counter in memory. Instead, a binary filtering subroutine is called. Upon completion of

this filtering, the bit detected four cycles ago is collected. If 0’s or 1’s are being counted

currently and a 0 or 1, respectively, is received, the current counter is simply

implemented. If zeros are being counted, it is checked to see if 128 0’s in a row have

been detected. If this is the case, then receive mode is exited and the data is transmitted.

If the opposite signal is detected, a transition has occurred. The RSF register is

incremented. If RSF is now at the last memory location, the sequence is too long to be

correct so receipt is aborted. Otherwise, a one is put in the new counter and the loop

continues.

Figure 5.24: Routine for receiving valid data


The binary filtering routine is intended to recover some of the sensitivity that is lost

by receiving at a much higher data rate. For instance:

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

1

Received Data

Figure 5.25: Example of corrupted data

Because the data rate will never be greater than 5000bps, if a detection of a 0 or 1

only lasts for one or two cycles, it is too short to be a real transition. These bits can safely

be assumed to be errors in detection.

A simple subroutine is listed below for doing this. In the subroutine, the STREAM is

compared to several known bit error patterns. If the STREAM matches one of these

known error patterns, it is corrected and the correct value is placed in stream. In this way,

knowledge that the actual data rate is less than the receive rate can be used in order to

help have more error free detection.

05512 RKE Repeater

Data in error

87

Figure 5.26: The binary filtering subroutine.

Once this is completed, the data is then set for transmission, and the transmit routine

is called.

The transmit routine is extremely simple. Because each location in RAM stores the

number of ones or zeros corresponding to that particular section of the waveform, the

task of the processor is merely to hold at high or low the output to the transmitter for the

specified amount of time. This is accomplished by recalling each of the RAM locations

where a number of 1’s and 0’s has been stored. The number is then decremented while

holding the TX output pin high or low. A delay corresponding to the data rate the data

was detected at is also contained in the path. The transmitter sends the recorded data until

0x7F is encountered, which indicates an end to the received data. When this is detected,


the receiver is turned back on, the antenna is switched back to the receiver, and the

transmitter is turned off.


Figure 5.27: The transmit routine


5.8 Impedance Matching Network

After the quarter wavelength antenna was chosen, it was necessary to match it to the

50 Ohm input impedance of the T/R switch. The miniNEC simulation showed that the

impedance of the antenna is 35.78-j0.798 ohms. In order to connect the antenna to the

T/R switch which has the impedance of 50 ohms, an LC matching circuit was designed.

The circuit consists of a 72nH inductor and a 98nF capacitor.

C 19 8 n F

1 2L1

72 n H

Switch Antenna

Figure 5.28: Impedance matching network


6. Work Completed

6.1 First Generation Receiver

To verify that the ideas for the repeater design will actually work, a basic receiver

circuit was designed and an implemented using ideal components. This receiver followed

the diagram shown below in figure 40. The design included a band pass filter a low noise

amplifier, a mixer and an intermediate frequency low pass filter.

Figure 6.1: First Generation Receiver

The band pass filter used in this design two simple tank circuits. The reason a tank

circuit was used instead of a band pass filter is that the size inductors available were not

small enough to build a proper band pass filter. A tank circuit is simply a capacitor and an

inductor in shunt. These act as a very wide-band bandpass filter depending on the values

used for the inductor and capacitor. To make the bandwidth a little more narrow a second

tank filter was added in series and separated by a .5Ω resistor. The reason the bandwidth

is so wide is because the load on the filter is so small. The bandwidth of the filter depends

entirely on the output resistor. The two tank filter circuit is shown below in figure 6.2 and

the simulation for this filter is in figure 6.3.

05512 RKE Repeater

Bandpass Tank Filter

Lowpass Filter

Function Generator

LNA MixerScope

92

C 12 . 7 p

C 22 . 7 p

1

2

L 1.1 uH

1

2

L2.1 u H

R 1

. 5

R 25 0

R 3

5 0V 11 V a c0 V d c

0

V

Figure 6.2: Tank Filter

Input Bandpass Filter

0.00E+00

1.00E-01

2.00E-01

3.00E-01

4.00E-01

5.00E-01

6.00E-01

1

2.34

4

5.49

5

12.8

8

30.2

70.7

9

166

389

912

2138

5012

1174

9

2754

2

6456

5

2E+0

5

4E+0

5

8E+0

5

2E+0

6

5E+0

6

1E+0

7

3E+0

7

6E+0

7

1E+0

8

3E+0

8

8E+0

8

2E+0

9

4E+0

9

1E+1

0

2E+1

0

5E+1

0

1E+1

1

3E+1

1

7E+1

1

2E+1

2

4E+1

2

9E+1

2

Fequency (Hz)

Mag

nitu

de (V

)

Figure 6.3: Tank Filter Frequency Response

The amplifier and mixer used for this receiver were both ordered from

www.minicircuits.com. The amplifier used for this receiver was MAN-1LN which has a

gain of 10dBm. The mixer used for this receiver was TUF-1LH. The amplifier was

powered by a 12.5 DC voltage and a maximum current of 40mA. The mixer was a

passive component. It is a ring diode mixer. It needs 10dBm in to operate effectively. It

has a LO input for the oscillator, a RF input for the input signal, and a IF output for the

mixed down signal. The output filter was just a simple capacitor in shunt with the output.

This capacitor acted as a very simple low pass filter which helped to prevent the image


http://www.minicircuits.com/

frequencies from interfering with the output signal. The final receiver circuit used for this

receive followed the schematic seen in figure 6.4.

Figure 6.4: First Generation Receiver Schematic

This schematic was built using the discrete parts described above. The circuit was

then tested using a function generator to simulate the input RF signal and to provide the

signal from the oscillator. The circuit was also simulated using a quarter wave antenna

for 315 MHz signal. This antenna was plugged in and the signal from the key fobs was

looked at.

All these simulations had a lot of noise. This is not what one would expect with an

ideal input, an ideal oscillator, and a very high quality mixer. However, there is still a

tremendous amount of noise in the output signal. The reason there is some much noise in

this system is because the system was constructed on a perforated board and the

components were connected with wires. This is a radio frequency system and therefore

the wires are acting as small antennas. The signal is interfering with itself. This is

because the original input signal is radiated out of the input line and is received into the

output line. To get a better and cleaner signal a printed circuit board with 50Ω lines needs

to be designed and used.


Even though the signal coming out of this receive is very messy it is still possible to

tell by the simulations that the signal being set was at 315MHz and that the signals are

being modulated using ASK modulation. These simulations verified the assumptions

made in the design for this repeater.

6.2 Work Planned

The next step then is to design a printed circuit board, with 50Ω lines, for the receiver

and repeat the experiment. This time more key fobs will be used and the key fobs will be

baked, frozen, and pressed many times to look at the frequency shifts due to the change

done to the key fob. The resulting data will allow us to modify our design to ensure that it

will work in all environments and remain stable even if the communicating key fob is not

stable.

This must be done before the design can be implemented. If the signal of multiple key

fobs is not used then there is no guarantee that the system will work as desired. Once the

range of frequencies and power levels has been recorded then the microcontroller code

can be finished. This is the only remaining design left.

Once all this is done then the implementation of the design can be done. The parts

need to be bought and a circuit board needs to be designed. The board needs to have 50 Ω

lines between the components to prevent a loss in signal power. After the board is

designed the circuit can be tested and the design can be modified to ensure that results

meet the customer’s specifications.


Bibliography

Books:

Vizmuller, Peter, RF Design Guide Systems, Circuits, Equations, Artech House, Boston, Ma., 1995

Carr, Joe, RF Components and Circuits, Newnes, Oxford, 2002

Carr, Joe, Secrets of RF Circuit Design Second Edition, McGraw-Hill Inc., New York, 1997

Balanis, Constantine, Antenna – Theory and Design, John Wiley & Sons Inc., New York,

1997

The A.R.R.L Antenna Book

MiniNEC Introduction to Modelling

Data Sheets:

rfRXD0420: http://ww1.microchip.com/downloads/en/DeviceDoc/70090a.pdf

PIC16F87: http://ww1.microchip.com/downloads/en/DeviceDoc/70090a.pdf

MAX1742: http://pdfserv.maxim-ic.com/en/ds/MAX1472.pdf

SAW Filter 162988: http://www.saw-device.com/pdfs/datasheets/162988%20315%20MHz%20RF%20Filter%20Data%20Sheet-P0.pdf

ADG919: http://www.analog.com/UploadedFiles/Data_Sheets/456430626ADG918_9_a.pdf

RKE Theory:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/1774

http://www.mwrf.com/Articles/ArticleID/7760/7760.html

http://www.mwrf.com/Articles/Index.cfm?ArticleID=7760&pg=2


http://www.mwrf.com/Articles/Index.cfm?ArticleID=7760&pg=2


http://www.maxim-ic.com/appnotes.cfm/appnote_number/1774

http://www.analog.com/UploadedFiles/Data_Sheets/456430626ADG918_9_a.pdf

http://www.saw-device.com/pdfs/datasheets/162988%20315%20MHz%20RF%20Filter%20Data%20Sheet-P0.pdf

http://www.saw-device.com/pdfs/datasheets/162988%20315%20MHz%20RF%20Filter%20Data%20Sheet-P0.pdf

http://pdfserv.maxim-ic.com/en/ds/MAX1472.pdf

http://ww1.microchip.com/downloads/en/DeviceDoc/70090a.pdf

http://ww1.microchip.com/downloads/en/DeviceDoc/70090a.pdf

Repeater Theory:


http://www.mobilecomms-technology.com/contractors/inbuilding/ems/

http://www.bvkhawaii.com/billyg/amareptr.htm

http://www.wtsn.binghamton.edu/bara/classes/Element2Summarypart1.pdf

PeopleWe would like to acknowledge the following people for their support, insight, and

advice in helping us to establish a preliminary design.

Dr. Phillips

Dr. Venkataraman

Professor Slack

Paul Jacobs

Jan Van Nekeerk


http://www.wtsn.binghamton.edu/bara/classes/Element2Summarypart1.pdf

http://www.bvkhawaii.com/billyg/amareptr.htm

http://www.mobilecomms-technology.com/contractors/inbuilding/ems/


Appendix A – FCC Regulations

The following FCC regulations govern the usage of the spectrum the repeater operates on:

[Code of Federal Regulations][Title 47, Volume 1][Revised as of October 1, 2003]From the U.S. Government Printing Office via GPO Access[CITE: 47CFR15.231]

[Page 745-746] TITLE 47--TELECOMMUNICATION CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION PART 15--RADIO FREQUENCY DEVICES--Table of Contents Subpart C--Intentional Radiators Sec. 15.231 Periodic operation in the band 40.66-40.70 MHz and above 70 MHz.

(a) The provisions of this section are restricted to periodic operation within the band 40.66-40.70 MHz and above 70 MHz. Except as shown in paragraph (e) of this section, the intentional radiator is restricted to the transmission of a control signal such as those used with alarm systems, door openers, remote switches, etc. Radio control of toys is not permitted. Continuous transmissions, such as voice or video, and data transmissions are not permitted. The prohibition against data transmissions does not preclude the use of recognition codes. Those codes are used to identify the sensor that is activated or to identify the particular component as being part of the system. The following conditions shall be met to comply with the provisions for this periodic operation: (1) A manually operated transmitter shall employ a switch that will automatically deactivate the transmitter within not more than 5 seconds of being released. (2) A transmitter activated automatically shall cease transmission within 5 seconds after activation. (3) Periodic transmissions at regular predetermined intervals are not permitted. However, polling or supervision transmissions to determine system integrity of transmitters used in security or safety applications are allowed if the periodic rate of transmission does not exceed one transmission of not more than one second duration per hour for each transmitter. (4) Intentional radiators which are employed for radio control purposes during emergencies involving fire, security, and safety of life, when activated to signal an alarm, may operate during the pendency of the alarm condition (b) In addition to the provisions of Sec. 15.205, the field strength of emissions from intentional radiators operated under this section shall not exceed the following:

------------------------------------------------------------------------ Field strength of Field strength of Fundamental frequency (MHz) fundamental spurious emissions (microvolts/meter) (microvolts/meter)------------------------------------------------------------------------40.66-40.70..................... 2,250............. 22570-130.......................... 1,250............. 125130-174......................... \1\ 1,250 to 3,750 \1\ 125 to 375174-260......................... 3,750............. 375260-470......................... \1\ 3,750 to \1\ 375 to 1,250 12,500.Above 470....................... 12,500............ 1,250------------------------------------------------------------------------


\1\ Linear interpolations.

[[Page 746]]

(1) The above field strength limits are specified at a distance of 3 meters. The tighter limits apply at the band edges. (2) Intentional radiators operating under the provisions of this section shall demonstrate compliance with the limits on the field strength of emissions, as shown in the above table, based on the average value of the measured emissions. As an alternative, compliance with the limits in the above table may be based on the use of measurement instrumentation with a CISPR quasi-peak detector. The specific method of measurement employed shall be specified in the application for equipment authorization. If average emission measurements are employed, the provisions in Sec. 15.35 for averaging pulsed emissions and for limiting peak emissions apply. Further, compliance with the provisions of Sec. 15.205 shall be demonstrated using the measurement instrumentation specified in that section. (3) The limits on the field strength of the spurious emissions in the above table are based on the fundamental frequency of the intentional radiator. Spurious emissions shall be attenuated to the average (or, alternatively, CISPR quasi-peak) limits shown in this table or to the general limits shown in Sec. 15.209, whichever limit permits a higher field strength. (c) The bandwidth of the emission shall be no wider than 0.25% of the center frequency for devices operating above 70 MHz and below 900 MHz. For devices operating above 900 MHz, the emission shall be no wider than 0.5% of the center frequency. Bandwidth is determined at the points 20 dB down from the modulated carrier. (d) For devices operating within the frequency band 40.66-40.70 MHz, the bandwidth of the emission shall be confined within the band edges and the frequency tolerance of the carrier shall be [plusmn]0.01%. This frequency tolerance shall be maintained for a temperature variation of -20 degrees to +50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. For battery operated equipment, the equipment tests shall be performed using a new battery. (e) Intentional radiators may operate at a periodic rate exceeding that specified in paragraph (a) of this section and may be employed for any type of operation, including operation prohibited in paragraph (a) of this section, provided the intentional radiator complies with the provisions of paragraphs (b) through (d) of this section, except the field strength table in paragraph (b) of this section is replaced by the following:

------------------------------------------------------------------------ Field strength of Field strength of Fundamental frequency (MHz) fundamental spurious emission (microvolts/meter) (microvolts/meter)------------------------------------------------------------------------40.66-40.70..................... 1,000............. 10070-130.......................... 500............... 50130-174......................... 500 to 1,500 \1\.. 50 to 150 \1\174-260......................... 1,500............. 150260-470......................... 1,500 to 5,000 \1\ 150 to 500 \1\Above 470....................... 5,000............. 500------------------------------------------------------------------------\1\ Linear interpolations.

In addition, devices operated under the provisions of this paragraph shall be provided with a means for automatically limiting operation so that the duration of each transmission shall not be greater than one second and the silent period between transmissions shall be at least 30 times the duration of the transmission but in no case less than 10 seconds.

[54 FR 17714, Apr. 25, 1989; 54 FR 32340, Aug. 7, 1989]


Appendix B – Bill of Materials

# Part Description Source Cost

1 rfRXD0420 Receiver Micochip $2.79 1 MAX1472 Transmitter Maxim $3.74 1 PIC16F87 Microcontroller Micochip $2.26 1 ADG918 T/R switch Analog Devices $1.07 1 162988a SAW Filter COM DEV $1.67 3 445-1268-1-ND .1uF Capacitor Degikey $0.09 1 311-1026-1-ND 220pF Capacitor Degikey $0.10 1 PCC2129CT-ND 680pF Capacitor Degikey $0.06 2 311-1153-1-ND 20pF Capacitor Degikey $0.10 1 490-2104-ND 270Ω resistor Degikey $0.89 1 M7825-ND 10uH inductor Degikey $0.54 1 TK4231-ND 20nH inductor Degikey $1.95 1 TK4229-ND 16uH inductor Degikey $1.30 2 DN10680CT-ND 60nH inductor Degikey $0.75

Total: $23.31


Appendix C – Complete Circuit Schematic


Documents

edge.rit.eduedge.rit.edu/content/OldEDGE/public/Archives/P05512/PDR.doc · Web viewIn spite of what figure (3.9) may look like, the data can be successfully demodulated and stored