MEHRMEHR CHANDCHAND POLYTECHNICPOLYTECHNIC COLLEGECOLLEGE,,

JALANDHARJALANDHAR

MINORMINOR PROJECTPROJECT SMALLSMALL FMFM RADIORADIO

SUBMITTEDSUBMITTED TOTO

MSMS. . PREETPREET KANWALKANWAL

MSMS. . KRITIKAKRITIKA CHAWALACHAWALA

SUBMITTED BYSUBMITTED BY

NAMENAME--VINAYVINAY KUMARKUMAR

RR..NONO.. 344/11344/11

NAMENAME-- RAVISHRAVISH KUMARKUMAR

RR..NONO.. 338/11338/11

CLASSCLASS-- EE..C.EC.E

INDEXINDEX

Introduction Block Diagram Of FM Receiver Circuit Diagram Operation Of The Circuit List Of Components

Resistors Capacitors Transistors Battery Inductor coil Antenna PCB Connecting wire Speaker IC

Advantage & Disadvantages ApplicationsModification Of FM

INTRODUCTION

In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant. In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input-signal amplitude. Digital data can be sent by shifting the carrier's frequency among a range of settings, a technique known as frequency-shift keying (FSK). FSK is widely used in data and fax modems, and can be used to send Morse code.[1] Radioteletype also uses FSK.[2] Frequency modulation is also used in telemetry, radar, seismic prospecting and newborn EEG seizure monitoring.[3] Frequency modulation is known as phase modulation when the carrier phase modulation is the time integral of the FM signal. FM is widely used for broadcasting music and speech, two-way radio systems, magnetic tape-recording systems and some video-transmission systems. In radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally-occurring noise.

BLOCK DIAGRAM OF FM RECEIVER

The block diagram of fm receiver

We have discussed the block diagram of AM super heterodyne receiver. The FM receiver is also a super heterodyne receiver which is similar to that of the AM receiver. The basic differences between the two receiver circuits are:

(i) The operating frequencies in case of fm are much higher.(ii) The limiting circuits and de-emphasis circuits are needed in

FM.(iii) The method of demodulation is entirely different in FM.(iv) The method used for obtaining AGC is also different in FM.

The basic block diagram of super heterodyne FM receiver is shown in fig. the main stages of FM receiver are as follows:

CIRCUIT DIAGRAM

The small fm receiver’s circuit

OPERATION OF THE CIRCUIT Perhaps this is one of the simplest and smallest FM radio receivers that can receive the FM stations available locally. Its simple design makes it ideal for a pocket sized FM receiver. The output of the receiver drives a head phone.

The circuit works off a small 4.5 volt battery or two 3.6 volt Lithium button cells.

The fm receiver section has two RF transistors T1 and T2 to detect the Frequency Modulated signals. Coil L1 and the trimmer capacitor form the tuned tank circuit to tune the receiver to the best FM station with strong signals. The signals are capacitor coupled through C2.

10K preset VR controls the volume to the input of the amplifier. IC1 is the micro power audio amplifier that works between 4.5 to 12 volts DC. The amplified sound can be heard through the low impedance head phone or small Mylar speakers.

FM radio coil

Coil is the important part of the FM tuner. It is made up of 18 SWG enameled copper wire. Wind 4 turns on a ball pen to get 0.5 cm inner diameter. Remove the enamel from the tip of the wire and solder tightly in the PCB. Trimmer and coil should be soldered very closely. Adjust the spacing of the coil winding if necessary to get the station clearly. Assemble all the receiver components as close as possible to get better result.

LIST OF COMPONENTS

Resistors

1. 22kΩ2. VR 10kΩ preset

Capacitor

1. 0.22pf

2. 0.1pf

3. 22.ooµf,25v

4. (VC) 22pf trimmer

Transistors

1. BF 492---(2)

Battery

1. 4.5 to 9.00 volt

Inductor coil

1. 18 SWG, 4T Air Core

Antenna

1. Telescopic Areal

Printed circuit bords (PCB)

1. General PCB

Connecting wire

1. Singal core wire

Speaker

1. 4 Ω speaker

Integrated circuit (IC)

1. IC LM 386

ADVANTAGE & DISADVANTAGES

ADVANTAGE

STATIC

AM receivers are much more subject to static and interference than FM receivers. FM stands for "frequency modulation," which means that the receiver depends on the rate that a radio wave changes for the information that it receives. AM receivers, on the other hand, rely on how strong or weak the radio wave is for their information. This difference allows for FM receivers to avoid the interference of such things as tall buildings and lightning.

AUDIO QUALITY

The range of sounds that can be heard over an FM frequency is noticeably larger than that broadcast by the AM frequency. An FM receiver will basically be capable of producing all the notes and sounds that are heard by the human ear. For music especially, this is a significant advantage, as all voices and sounds will be rendered accurately, as they were meant to be heard.

VARIETY OF STATIONS

After widespread adoption of FM during the 1950s, more and more music became available through FM receivers. While competitors such as the CD and satellite radio have become popular, an FM receiver is still an accessible way to listen to a stream of free portable music, and to introduce yourself to new artists and content. An FM receiver is a great device for any person who loves music.

DISADVANTAGE

The biggest problem with FM is the potential for outside interference. Although 40 channels (narrow band) in the 72-76 MHz bandwidth have been set aside by the FCC for use in FM systems, outside interference may occur with nearby radio stations, pagers, police band, and construction walkie talkies. Sometimes devices ‘drift’ from their targeted frequencies and must be adjusted to correct for this. . However, newly developed 216MHz systems are now available that should alleviate this intereference problem.

This system is also not a secure system. If you can leave the room and still pick up the signal, this means others could pick it up, as well. If security is an issue (as in jury deliberations or in high-tech company business) an infrared system would be the system of choice (discussed in the next section).

Receivers are required for everyone. These receivers vary in quality with the manufacturer. Only purchase these systems from companies that will help you troubleshoot and that have a trial period and return policy.

If you purchase multiple systems at separate times, color code or number transmitter and receiver pairs. Remember, the pairs must be tuned into the same channel.

Finally, if multiple systems are being used in close proximity, there must be at least one free channel between the separate systems to prevent interference in adjacent rooms.

APPLICATIONS

MAGNETIC TAPE STORAGE

FM is also used at intermediate frequencies by analog VCR systems (including VHS) to record the luminance (black and white) portions of the video signal. Commonly, the chrominance component is recorded as a conventional AM signal, using the higher-frequency FM signal as bias. FM is the only feasible method of recording the luminance ("black and white") component of video to (and retrieving video from) magnetic tape without distortion; video signals have a large range of frequency components – from a few hertz to several megahertz, too wide for equalizers to work with due to electronic noise below −60 dB. FM also keeps the tape at saturation level, acting as a form of noise reduction; a limiter can mask variations in playback output, and the FM capture effect removes print-through and pre-echo. A continuous pilot-tone, if added to the signal – as was done on V2000 and many Hi-band formats – can keep mechanical jitter under control and assist timebase correction.

These FM systems are unusual, in that they have a ratio of carrier to maximum modulation frequency of less than two; contrast this with FM audio broadcasting, where the ratio is around 10,000. Consider, for example, a 6-MHz carrier modulated at a 3.5-MHz rate; by Bessel analysis, the first sidebands are on 9.5 and 2.5 MHz and the second sidebands are on 13 MHz and −1 MHz. The result is a reversed-phase sideband on +1 MHz; on demodulation, this results in unwanted output at 6−1 = 5 MHz. The system must be designed so that this unwanted output is reduced to an acceptable level.

SOUND

FM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by early digital synthesizers and became a standard feature in several generations of personal computer sound cards.

RADIO

An FM signal can also be used to carry a stereo signal; this is done with multiplexing and demultiplexing before and after the FM process. The FM modulation and demodulation process is identical in stereo and monaural processes. A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals). For a given signal strength (measured at the receiver antenna), switching amplifiers use less battery power and typically cost less than a linear amplifier. This gives FM another advantage over other modulation methods requiring linear amplifiers, such as AM and QAM.

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. Normal (analog) TV sound is also broadcast using FM. Narrowband FM is used for voice communications in commercial and amateur radio settings. In broadcast services, where audio fidelity is important, wideband FM is generally used. In two-way radio, narrowband FM (NBFM) is used to conserve bandwidth for land mobile, marine mobile and other radio services.

FM_Broadcast_Transmitter_High_Power

MODIFICATION OF FM

HOW TO MODIFY AN FM RECEIVER

When using an FM radio receiver, you can listen to your favorite local radio stations. These receivers come in all shapes and sizes, ranging from small, portable devices to larger, stereo units. When using an FM receiver, you have several options for modifying the equipment, ranging from the speakers you have connected to the equipment to being able to hook up outside audio devices to your FM receiver

INSTRUCTIONS

Check your FM receiver for an auxiliary port. This is a red and white RCA input connection, which allows you to hook up outside devices to your receiver, such as a DVD player or television. Plug the RCA audio cables into the "Audio Out" ports of the desired source equipment, then insert the opposite ends of the cables into the "Aux" ports of your FM receiver. When you select the "Aux" option on your receiver, it plays back the audio from the hooked up hardware.

Purchase new stereo speakers if your FM receiver allows for stereo speaker hook up (there are two wire input connections on the back of the receiver for this). You can buy any size or shape of speakers to fit your needs. Once you have the speakers in place, insert the wire from the speakers into the speaker connection ports on the FM receiver.

Twist off your current antenna (if you have a detachable antenna) and connect a new, amplified antenna (purchased at most electronic stores). This improves your audio reception and increases the number of FM stations to which you can listen.