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A Tropospheric Scattering, Non-Line-of-Sight

(NLOS) Wireless Data Communications Link

Final Report

Fall Semester 2009

Prepared to partially fulfill the requirements for ECE401

Department of Electrical and Computer Engineering

Colorado State University

Fort Collins, CO 80523

By:

Jassim Makki

Naif Alhujilan

Rashid Al-Mohannadi

Report Approved: ___________________________________

Project Advisor

___________________________________

Senior Design Coordinator

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Abstract:

Meteors could be used to establish point to point data link. Meteors hit the atmospheric layer

everyday and provide an opportunity to scatter waves and thus establish a communication link.

The task is to establish this link between two points 67 miles apart at 50MHz. 67 miles is

considered to be a short distance for meteor scattering and this project testify if it is possible.

However, the link must support at least 20 signal-to-noise-ratio.

This project started with installing a test bench that repeatedly transmits waves at 50 MHz and

the task is to find if there is any meteors enhancement. This includes using an antenna that has

low angle radiation and high angle radiation that would permit meteor scattering and

tropospheric scattering. Then, the received signal must be analyzed to find out if there is

meteor scattering. If not, the system must be analyzed to find out what is missing to establish

this link.

However, the received signal was low and no varying which means that there is no meteor

scattering. This is due to two reasons. The first reason is that the distance between the two

points is limiting the probability of finding meteors that could be used for scattering. This is

similar to shooting thru a ring that is located far away. However, it is still possible to do it if

more directed antennas with higher gain is used. On the other hand, this experiment showed

us that there is a high noise at 50MHz which resulted in a low SNR=1.5. This noise is mainly

because of man-made noise.

Tropospheric scattering is another option. It can be observed at frequency range of 144 MHz up

to 10 GHz. The path loss increases as the frequency increase, so in this system, we used

simulation software to help us choose the best frequency to operate at.

432 MHz is a good choice. The SNR is not as desired; however, the system can be adjusted to

increase SNR. Studies done and data collected are very promising that this system will operate

successfully.

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Supervisors:

Name: John Steininger

Field: Electrical Engineering

Biography:

Mr. Steininger is an Electrical Engineer, the head of the senior design team, and the one who

own the idea of this project. So every this project is owned and all the information mentioned

in this document to reference to Mr. Steininger.

Contact: E-mal: jms@frii.com

…………………………………………………………………………………………………………………………………….…………

Academic Advisor:

Name: Professor Ali Pezeshki

Field: Electrical Engineering

Biography:

One of Professor Pezeshki interests’ is wireless communications, since our project has such

subject, he was introduced to it and wanted to be as involved as possible and he was really

helpful.

Contact: pezeshki@engr.colostate.edu

……………………………………………………………………………………………………………………………………………………

Academic Advisor:

Name: Professor Rockey Luo

Field: Electrical Engineering

Biography:

Professor Rockey Luo has an interest in communication networks, and he was introduced to

this project for this reason and he was really helpful.

Contact: rockey@engr.colostate.edu

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Students:

Name: Jassim Makki

Contact: jassim@rams.colostate.edu

………………………………………………………………………………………………………………………………………………

Name: Naif Alhujilan

Contact: ee.nayef@gmail.com

………………………………………………………………………………………………………………………………………………

Name: Rashed Al-Mohannadi

Contact: raa87@rams.colostate.edu

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TABLE OF CONTENTS

Title ……………………………………………………………………..………………………..……………………………………….. 1

Abstract ……………………………………………………………………………………..……………..………………………....... 2

Supervisor information …………………………………………………………………………..................................... 3

Student information ……..………………………………………………………………………………………………..…....... 4

Table of Contents …………………………………………………………………………………..................................... 5

List of Figures and Tables ………………………………………………………………………………………………..…....... 6

I. Introduction …………………………………………………………………………………………………………………...……. 8

II. Approach …………………………………………………………………………………………………………………………….. 9

III. Transmission station ……………………………………………………………………………………………………….… 10

IV. Receiver station ………………………………………………………………………………………………………………… 14

V. Radio Propagation study ……………………………………………………………………………………………………. 14

VI. AFSK Modems …………………………………………………………………………………………………………………… 15

VII. Results …………………………………………………………………………………………………………………………….. 16

VIII. Options …………………………………………………………………………………………………………………………… 19

IX. Modems ……………………………………………………………………………………………………….………...……….. 20

X. Simulation …………………………………………………………………………………………….…………………………… 23

Results at 432 MHz ………………………………………………….………………………………………………… 23

Results at 1270 MHz ……………………………………………………………..…………………………………… 23

Choice ………………………………………………………………………………………………………………………… 24

XI. Antenna ……………………………………………………….…………………………….………………………..…………… 25

XII. Current Status ………………………………………………………………….……………………………………………… 26

XIII. Recommendation for project continuation …………….………………………………………………………. 27

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IXV. Conclusion ………………………………………………………..……………………………………………………………. 27

References …………………………………………………………………………………………………………………………….. 28

Appendix A – Abbreviations …………………………………………………………………………………………………… 29

Appendix B - Budget ……………………………………………………………………………………………….……………… 30

Appendix C - Acknowledgment ……………………………………………………………………………………………… 31

LIST OF FIGURES

Figure 1: Communication Channels for VHF Meteor Scatter project ………………………………………… 9

Figure 2: Morse code diagram ………………………………………………………………………………………………. 11

Figure 3: Block diagram …………………………………………………………………………………………………………. 12

Figure 4: Flow Chart ………………………………………………………………………………………………………………. 13

Figure 5: Noise vs. Frequency ………………………………………………………………………………………………… 15

Figure 6: Simulation Results …………………………………………………………………………………………………… 16

Figure 7: power Pattern …………………………………………………………………………………………………………. 17

Figure 8: MS & TS …………………………………………………………………………………………………………………… 18

Figure 9: Modems & noise injection ………………………………………………………………………………………. 20

Figure 10: Summer Circuit …………………………………………………………………………………………………….. 21

Figure 11: SNR vs. BER ……………………………………………………………..……………………………………………. 22

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Figure 12: Simulation at 432 MHz ………………………………………………….…………………………………………. 23

Figure 13: Simulation at 1270 MHz …………………………………………………………………………………………….. 24

Figure 14: Yagi Antenna …………………………………………………………………………………………………………. 25

Figure 15: Power pattern of Yagi Antenna …………………………………………………………………….………. 25

Figure 16: audio oscillator ………………………………………………………………………………………….………….. 26

LIST OF TABLES

Table 1: Budget ……………………………………………………………………………………………………………………… 30

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I. Introduction:

In this project we will explore the possibility of building a point to point link with meteor scatter

that would help to develop a communication system that operates at a very high frequency of

fifty mega hertz (50 MHz). This frequency would help study the different propagation modes,

like meteor scattering to improve this wireless communication system. This physical system

would help us as engineers, rather than being students to experience real life obstacles that

field engineers encounter. Furthermore, thanks to our super visor we were able to get sense of

how to deal with real life design approaches and how making mistakes is more desirable to

learn from them.

Meteor scattering is a radio propagation mode that utilizes the ionized trails of meteors where

a short path of communication can be establish between two communication stations that can

ranges up to 2250 kilo meters or about 1400 miles. When meteors enter the upper atmosphere

they burn up creating a trail of ionized particles that can keep on for several seconds, those

particles in the ionized trails can be very dense that can be used to reflect radio waves. The

intensity of the ionized trails determines the frequencies that can be reflected which

sometimes ranges between 20 MHz and 500 MHz .when it comes to how much of a distance a

communication is established, even though the trails exists only for fractions of a second to few

several seconds which indicate a small window of communication, there are some factors that

need to be considered ; which includes the altitudes at where the ionization is shaped , location

of the falling meteor over the earth’s surface , the meteor’s angle of entry to the upper

atmosphere and the location of the communication stations where the channel is desired to be

established.

One of the applications of Meteor Scatter communication is an automated system called

SNOTEL of snowpack where it related to climate sensors. SNOTEL is the acronym for SNOwpack

TELemetry which is defined as network of computers, people, communication devises,

microprocessors and sensors to collect hydro meteorological data. SNOTEL was the motivation

for using meteor scatter in this project. This data that SNOTEL collects can include the

measurements of snow and water content, temperature and accumulated snow or rain. This

application of meteor scattering is the one of the motivations to build such a communication

system.

After introducing the project and some back ground of Meteor scatter, this report will explain

the different approaches of the main goal which is building the link between two

communication stations with our physical system along with our current results.

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Figure 1 shows a friendly painted picture of the project; where it can be shown the

communication channels using meteor scattering.

Figure 1: Communication Channels for VHF Meteor Scatter project.

II. Approach:

In this project we had some outlined planning on how we can build a system that can act as our

SNOTEL; the approaches can be ordered as follows with a brief enlightenment for each

approach;

First, transmitting a signal from a remote signal to a local place in Fort Collins, this step includes

the following procedures to achieve this objective.

1- Build a test bench that includes the automated station at the remote site where the

transmission takes place.

2- Build a receiver satiation in Fort Collins.

From the previous approach, it can be concluded that in this approach we are building the point

to point communication stations where the desired channel of communication using Meteor

Scatter will take place.

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Then, after building our radio stations; data about the transmitted signal from the remote

station is going to be collected and analyzed to monitor any enhancement caused by meteor

scattering. This approach can be titled as Radio propagation study.

After that, we will be building a mathematical model that would help analysis and make use of

our results of the collected data, mentioned previously.

Finally, we are going to build modems that can communicate using the channel we aimed to

establish. This was a rough sketch of what the report is going to be talking about. The following

is going to be a more detailed description of how those approaches were made along with their

results, what problems that each step had and new decisions that were made beside the ones

that were mentioned here.

III. Transmission station:

To start with, we had to build a transmission station located at John’s cabin NW of Fort Collins.

The transmission will be controlled by a micro controller chip that transmits known signal coded

into Morse code. Morse code is a type of character encoding that transmits telegraphic

information using rhythm. Morse code uses a standardized sequence of short and long

elements to represent the letters, numerals, punctuation and special characters of a given

message. The short and long elements can be formed by sounds, marks, or pulses, in on off

keying and are commonly known as "dots" and "dashes". The speed of Morse code is measured

in words per minute (WPM) or characters per minute.

In our project, the dots and dashes are transmitted by on-off keying controlled by the micro

controller and have a speed of about 10 WPM.

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Figure 2: Morse code diagram.

To better understand the transmission station, we shall start with this block diagram.

A DC\DC divider will be used to reduce the 24v, coming from the battery bank, to about 3v to

supply the micro controller chip (MC). MC chip will be monitoring the battery bank while

sending the signal, if the battery bank drop below 22v, MC chip will turn the whole system off

through the relay board till the battery is solar charged again.

The relay board is simply two switches controlled by MC to turn off the amplifier and to

disconnect the battery bank so that no power keeps being consumed.

Both MC chip and key switch will be used to send the Morse coded signal by switching the

transceiver on and off. This signal will be passed through amplifier and then to the antenna.

The amplifier will be turned on and off by MC chip and has a 12v supply coming from the main

battery bank.

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Figure 3: Block diagram

Amplifier

Antenna

12 V

24 VDC/DC: reduce the 24 V to the

Value (power supply for mC)

Divider: reduce the 12 V to a measurable voltage for

The mC, if the battery charge is low the mC will turn

Off the system till the battery is charged.

Key

Switch

MC

Relay

Board

Switch

Switch

DC/DC: reduce the 24 V to 12 V

(charge up the battery)

Remote: to switch between receive

and transmit mode

Switch: to disconnect

24v battery from DC/

DC till it charges up, if

needed.

Disconnection is

through the relay

board.

PTT

Push-to-talk

Switch:

To switch

between

receive and

transmit

mode

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The following graph is a flow chart that summarizes the steps in transmission.

Figure 4: Flow Chart

The antenna used to transmit the signal called (Yagi antenna). It has a central element and cross

elements above the central. It is an end fire antenna and has a power pattern directed to the

sky at 16 degree above the ground.

The system was completely installed and running by Oct. 15th, the signal was successfully

received even thou we had to operate on 150W instead of 50W. This means we will be

consuming more power than what we thought, but the battery bank was able to handle that

extra usage of power.

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IV. Receiver station:

The signal is received here in Fort Collins at John’s house. We will capture the signals

transmitted from the beacon using a commercial, amateur radio transceiver. This radio is a very

sensitive, frequency selective power meter that can be tuned to the beacon transmit frequency

and can measure the received power from the beacon over time. The antenna used to capture

the signal is a loop antenna, which has an omni directional pattern to receive the signal in spite

of the direction it is coming from.

A program written in C- sharp will get the data from the transceiver and save it in a file. These

data will be collected over days and samples will be measured and saved over periods of time

as desirable. Then, this data will be used to study and analyze the channel we are using.

V. Radio Propagation study:

After data was collected using the test bench, they must be analyzed to find out what type of

scattering in the link. At 50 MHz, there are many propagation mechanisms including

tropospheric scattering, meteor scattering and ionospheric scattering. These mechanisms have

different observations which would lead the type of scattering or reflection is used.

Meteor scattering is usually observed by a sudden variation on the received signal. Meteors hit

the top atmospheric layer and it creates an ionized trail forming a dense area that would

reflect. However, this dense area lasts for a few seconds or even a fraction of a second and this

explain why enhancement in received signal lasts for a few seconds. On the other hand,

meteors hit the atmospheric layer every day and the chance of getting more enhancement

increases if the wave propagating travel long distance to get a better probability of reflecting

from multiple meteors. An average distance of meteor scattering is about 2250km and our

system has two points that are 107km apart. This is one of the challenges in this design that this

short distance provides a small opportunity of observing meteors because the transmitting

station will be shooting at a small window creating a small probability of hitting a meteor.

Another type of scattering available at 50MHz is tropospheric scattering. In this mechanism,

waves are reflected at the lowest atmospheric layer called troposphere layer. This layer extends

from the earth’s surface to a height of 7 miles. In this layer, there are inhomogeneous places

called ‘blobs’ which has a different reflection index from air causing waves to be reflected. This

layer has the advantage of being available at all time which would help to test our system if it’s

directed towards this layer. As mentioned above, the troposphere layer exists at the lowest

part of the atmosphere layer which requires a low angle radiation. Experiments have shown

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that the best results when waves are transmitted at low angle and found that for each angle

above in the vertical plane costs 9-12 dB. Tropospheric scattering works from 50 MHz to 10GHz

which is another feature of this mechanism.

Noise at 50MHz is due to different sources. It includes atmospheric noise and man-made noise.

But as this plot shows man made noise is the dominant. It is at -110dBm at 50 MHz.

Figure 5: Noise vs. Frequency

VI. AFSK Modems:

Once the channel is analyzed and the link is established, modems will complete this link and

make it useful. Modems will be useful to control the receiver station since it can communicate

with digital devices. Modems that will be used are Audio Frequency Shift Keying modems.

These modems will be connected to a radio to receive or transmit information. We built these

modems starting from soldering resistors and capacitors to installing IC chips. These modems

come with full instructions on how to install them from the manufacturer ( www.tnc-x.com ).

However, it is good to build these modems to understand how they function. The modem

consists of an FSK modulator and demodulator that is connected to a microcontroller which

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controls the whole modem and control the flow of data from the modulator to memory and

then to the output using a USB connection. The software that controls the modem is obtained

from the manufacturers and it is editable. However, these modems require at least SNR= 20 dB

to function correctly which adds another constraint to our link.

VII. Results:

After building the test bench, we measured the signal strength using the receiver station and

recorded (-107dBm). This received power is very low and implies that there is something wrong

with the link. It could be a problem with the equipments or some other source of error. To

verify this recorded power, simulation software of the link would be the best start. Using free

simulation software called Radio mobile, the link was simulated and the result was close to that

received power.

Figure 6: Simulation Results

As seen from that last figure, Rx=-103dBm. Therefore, the recorded power is correct and this

conclusion shifts our attention to figure out another possible source of error.

Although the received power is low, the signal strength is still measureable and should be

analyzed to work towards the project goal which is finding if there is meteor scattering

communication. After monitoring the signal strength for a week, there was no enhancement

and the signal strength was the same. As found in the literature about meteor and tropospheric

scattering, no variation in the received signal means no meteor scattering and the dominating

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scattering is tropospheric scattering. However this could change if we monitor the signal for a

longer time and with different set of equipments that would transmit signals at high angles.

After reaching a conclusion about the type of scattering for the signal transmitted over this

short period, our attention moved to analyze the system further and find out what is behind

this low received power. One possible source of error is the antennas used at either the

transmitting station or the receiving station. Starting with the transmitting the antenna, a

radiation pattern was obtained for a 4-element Yagi antenna that is 6 meters (the same

wavelength) above ground.

Figure 7: power Pattern

This radiation pattern was the missing key to explain the low received power. As seen from the

figure, the pattern shows no low angle radiation which is crucial for our dominant tropospheric

scattering. To emphasize, tropospheric scattering needs low angle radiation, the lower the

better. This analysis was used to analyze the whole system again.

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Figure 8: MS & TS

Above is a diagram for our link, it shows that the transmitting antenna max gain is at 16.2 and

the tropospheric layer, given the altitude at the transmitting station, is at lower angle. Most

likely, the transmitting antenna is missing the tropospheric layer. The reason behind the

nonexistence of low angle radiation is the height of the antenna which is only 6 meters and this

is the wavelength of our transmitted waves. This low height compared to the wavelength

causes ground reflection that prevents low angle radiation. The best solution is to raise the

antenna using a tower to get low angle radiation.

After analyzing the low signal strength, there is another problem to analyze which is the high

noise measured at the receiving station. The noise as mentioned earlier was -105dBm and it is

mainly due to man-made noise at 50MHz. This creates a problem and a new challenge since our

design constrain is SNR=20dB. Given our noise and received power, SNR=1.5 which means that

the system needs a revolution to obtain the requirement.

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VIII. Options:

The main problem is manmade noise which badly impacts the SNR. To overcome this problem

we have two options:

The first option is to continue trying with meteor scattering. Since the scattering is dominated

by tropospheric scattering, the angle of radiation of the antenna should be increased to point

skywards so that the radiation can pass the tropospheric without reflecting.

The transmitted power also should be increased to achieve higher SNR, but even with the

increased power, the SNR will not be high enough to be able to use the current modems, so this

mean that the modems will have to be changed as well.

This option will maintain the idea of Meteor Scattering, however, it is not efficient because the

needed transmitted power will not be easily generated.

The second option is to move to tropospheric scattering at higher frequency. Moving to higher

frequency means moving to a region where the manmade noise is much lower than the current

noise. This criteria will help to achieve the desired SNR (20 dB) and since noise is main problem,

we decided to focus on the second option and build our system using the advantages of

troposphere layer.

Tropospheric scattering provides benefits such as:

1- Troposphere layer reflects the signal because of the differences of density and moisture

at that region, so the scattering will be available all the time.

2- With troposhperic scattering, the system can use higher frequency unlike with meteor

scattering and that helps in noise reduction.

3- Tropospheric scattering requires a low radiation angle, and constructing such antenna

with higher gain will be easier and possible with the same equipments and power

supplies we have.

4- The distance between the two ends in our system is about 62 miles and Tropospheric

scattering provides a good communication channel over distances between 70 to 600

miles, while meteor scattering works better with greater distances.

Because of all of these reasons, we decided to move forward in our project and build it at

higher frequency (432 MHz) using tropospheric scattering.

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IX. Modems:

Here we built two tnc-x modems and a summer circuit to measure the signal to noise ratio and

the bit error rate. We injected noise simulated by software into the summer circuit between

the two modems as can be seen in figure 9.

Figure 9: Modems & noise injection.

The noise source is basically a white noise simulated and injected to the summer circuit during

the communication between the two modems to measure the signal to noise ration they are

operating on and to see at what noise level they can stop communicating. However, the noise

should be injected in a way that does not eliminate the sent signal totally but disturb it in a

controlled way so that BER at a given SNR is calculated.

In the diagram below, Where = 250 Kohms , and act as voltage dividers to achieve 2.5

volts. Furthermore, the low pass filter in figure 10 is used to block any high frequencies that can

affect the circuit. The 1uF capacitor is used to block any DC signal to the other modem. It was

mentioned that we used free software to inject noise but during our measurements we also

used a radio to simulate the real physical system that would have a low pass filter that filters

out the incoming signal.

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. Figure 10 is the summer circuit that was used.

AC

2.5 Kohm

10 ohm

RfR1

R2Rf

Rf3 uF

0.1 uF

1 uF

3 uF

Rf= 250 Kohm

R1:R2: voltage divider

to achieve +2.5 v

VDD: +5 v

+

-

Low pass filter

Modem 1

LM 741

To modem

2

Force output

to have 0v

DC

+ 2.5v

Summer circuit:

Adding noise to the signal going from

modem 1 to modem 2:

Noise

source:

Radio with

15KHz

Low Pass

filter

600600

So that both input signals

see the same impedance

Figure 10: Summer Circuit.

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After building our modems and summer circuit we came up with the following measurements:

At higher noise the communication between the two modems stopped while decreasing

the noise the commutation ran smoothly. The bit error rate is calibrated as follows in figure 11:

BER

SNR in dB

10 dB

Infinity

zero

Figure 11: SNR vs. BER

Some notes about figure 13 calibration:

- When start to send information from modem 1 ; the output signal = 31.3 mili volts and it

is 26 mili-volts otherwise.

- The result of SNR = 10 dB is from a noise value of 10 mili-volts RMS , that is

Where Vs is the source voltage and Vn is the noise voltage.

- At a noise level of 10 mili-volts the communication between the modems are always

succeeding in transmitting and receiving.

The bit error rate reaches infinity when operating in signal noise ratio of 10dB, where it reaches

zero at signal to noise ratio above 10 db. So where are aiming to operate at 15 dB which is

much better than the 20 dB SNR mentioned earlier which make our system even better.

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X. Simulation:

Using the same program, Radio Mobile, we simulated our system using two frequencies to

observe the differences and benefits of each frequency. We chose 1.270 GHz and 432 MHz.

Path loss increases as the frequency increases, so we decided to simulate our system at these

two frequencies and calculate the SNR associated to each frequency.

Results at 432 MHz:

The program shows a Path loss of 195 dB. At this frequency, the system transmits 70 W. the

calculated man made noise at the receiver end is 8 dB. Given these information, we calculated:

SNR = 5.5 dB.

Figure 12: Simulation at 432 MHz

Results at 1270 MHz:

The program shows a Path loss of 207 dB. At this frequency, the system transmits 40 W. the

calculated man made noise at the receiver end is 1 dB. Given these information, we calculated:

SNR = 2 dB.

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Figure 13: Simulation at 1270 MHz

Choice:

432 MHz combine low man made noise and acceptable path loss. SNR= 5.5 dB, which is lower

than desired, but we can increase it by having higher antenna gain. We will continue this design

and will implement it at this frequency.

The SNR is low due to having a mountain in front of the cabin. This mountain forces the

antenna to have higher elevation angle. In tropospheric scattering, each degree costs between

9 – 12 dB of loss. This can be avoided by increasing the height of the antenna, but because the

mountain is very close (3000 meters) increasing the height will not improve the SNR much.

Once the cabin is accessible, we will install the beacon interface, put the antenna and measure

the real SNR. If the SNR improved enough with the new antenna (11 dB or more), the system

will be ready to operate and go to a new phase. If the SNR is still below 11 dB, then we will look

at the options available to increase it (discussed in the recommendation for project

continuation section).

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XI. Antenna:

In this new path, the signal

will be transmitted using Yagi

antenna with higher gain.

Yagi antenna is easy to

construct. Even though the

dimensions of the elements

are critical, with some care,

we can build it and achieve

higher gain (12 dB).

We will be using 11 elements

antenna designed to operate

at frequency range of 428 to

435 MHz. Ground will cause

the elevation angle

(Maximum gain angle) to be

more than the desired, and

the only way to avoid this is

by elevating the antenna

several wave lengths above

the ground. Operating at 432 Figure 14: Yagi Antenna

MHz corresponds to a wave length

of 0.69 m which means elevating the antenna several wave lengths above the ground is easy to

achieve.

Figure 15: Power pattern of Yagi Antenna

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XII. Current Status:

Currently we are working on an audio oscillator circuit that is going to be implemented in the system. The Audio oscillator will help to convert the 1’s and 0’s coming from the microcontroller to an audio tone because our radio will only receive audio tones. The picked design of the audio oscillator is shown below in the figure.

Figure 16: audio oscillator

Furthermore, we have built the eleven element antenna and we are working to match its impedance to the transmission line. After that we well go to the cabin to implement the system and measure our new signal to noise ratio.

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XIII. Recommendation for project continuation:

The simulation result shows that our system achieved 5.5 SNR at 432MHz which is

unsatisfactory for the modems to work. There are many options to continue working on this

project to achieve a better data link.

1. Build an array of antennas at both ends. For each element added in the array, 3

dB is achieved in excess of current SNR.

2. Develop the modems to work at low SNR and then it could be developed to use

one of the coding schemes which could results in doubling SNR. For example, the

modems could be designed to send each bit 2 times which results in doubling the SNR

but the minimum required SNR must be achieved.

3. On the applications side, this data link could be utilized to control the remote

site (cabin). This link could be designed to control the heating system in the cabin and to

control water level on the lake available at that site. Also, it could be used as a

communication link since there is no cellular service at the remote site. This cabin is not

accessible at winter season and most of spring season due to snow. So, this link could be

designed to check the snow level and whether it is accessible.

4. The main obstacle that we faced in this project is the poor location of the cabin

since it is located 3km away from Green Mountain which is on the line-of-sight path. To

overcome this problem, a repeater at the mountain summit would increase SNR by

more than 10 dB. This repeater would make this link as a line of sight path for the short

distance from the cabin to the mountain and then another long line of sight path from

the mountain’s summit to the receiver end in Fort Collins. Also, the long line of sight

path might take advantage of tropospheric scattering since the scatter angle will be

much lower than before.

IXV. Conclusion:

This project is a communication problem that reflects real life engineering experience. We

learned how to identify, solve and approach a problem and we got the opportunity to be part

of this project which we would like to continue next semester to achieve the goal of it.

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REFERENCES

[1] David, H.H. “A new approach to long range communications”. IEEE, Vehicular

Communications, Aug 1961.

[2] Darnell, M. Riley, N.G. Melton, D. “Tropospheric scatter propagation in the low-VHF

band”.IEEE, Antennas and Propagation, 1991.

[3] Hansen, John. “How to build AFSK modems”. www.tnc-x.com.

[4] Joint Technical Advisory Committee. “Radio Transmission By Ionospheric and Tropospheric Scatter”.

IEEE, Proceedings of IRE, 1960.

[5] PolyZou, J. Sassler,M. “Path-Loss Measuring Techniques and Equipment”. IEEE, Communication

Systems, 1960.

[6] Preben-Hansen , Palle . “Everyday VHF, UHF, and SHF propagation 700 km DX anytime using troposcatter.” [April,13 . 2010].

[7] Roos, Andrew. “A Simple 70cm Satellite Antenna”.

www.qsl.net/zs1an/weekend_antennas_4.pdf. 2005

[8] “Smooth Tone Clickless CW Sidetone Generator Electronic Circuit.”

http://www.circuitsarchive.org/index.php/Smooth_Tone_Clickless_CW_Sidetone_Generator,[

April,20.2010].

[9] Willis, Mike. “Propagation Tutorial.” http://www.mike-willis.com/Tutorial/PF9.htm ,

[April, 1.2010].

-29-

Appendix A - Abbreviations:

BER: Bit Error Rate.

MC: Micro Controller.

SNOTEL: SNOwpack TELemetry.

SNR: Signal to Noise Ratio.

VHF: Very High Frequency.

WPM: Word Per Minute.

-30-

Appendix B - Budget:

Electrical engineering department provides 50$ for each student per semester, however, the

project is funded by our supervisor John Steininger. The total money spent was 1244 $. Most of

the money went into affording the beacon interface equipments. Also about 250$ was spent to

buy the AFSK modems.

The adjustment done to the design this semester added additional cost. New yagi antennas

with higher gain at cost of 200 each. The power amplifier was changed to operate at 432 MHz

and that added a cost of 50 $.

The next table shows the total money spent in details.

Part / Hard ware Expenses in $

24V Divider

3

Key Switch

2

Relay Board

10

USB Supply

5

Misc. HW

15

Transmitter

185

Power Distribution

95

DC/DC Converter

45

Power Amplifier

270

Antenna, 4 element yagi 158

Lightening arrestor

50

Coax

92

Mast bracket

20

Connectors

30

3 modems

204

3 soldering irons

60

New antenna and power amplifier

4 450

Total: 1694

Table 1: Budget

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Appendix C - Acknowledgment:

At the end, we would like to thank our supervisors, John Steininger, Prof. Rocky Luo and Prof. Ali

Pezeshki for providing this opportunity and for helping us through all the semester. They have

been good teachers and good team leaders. We learned about communication and lived a real

life experience.