Mini Project Report

MINI PROJECT REPORT

FM RECEIVER

ELECTRONICS & COMMUNICATION ENGINEERING

EC 435- ELECTRONICS SYSTEM DESIGN LAB

Submitted by

D.PALANICHAMY

A.VINOTH SETHURAM

R.STEPHEN

RM.RENGANATHAN

S.T.VIVEK

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

SHANMUGANATHAN ENGINEERING COLLEGE,

ARASAMPATTI-622 507.

ABSTRACT:

FM means frequency modulation. In this method the radio frequency is converted to depends on the audio signal. AM receiver has more noise. For example spark due to spark plug in motor vehicles also added to the sound. This spark s are not added in FM receiver. FM accommadate the channels within the frequency 88MHZ to 108 MHZ. FM broadcast the program over 100 Kilometer. In AM broadcasting the modulating AF frequency is limited to 5 KHZ from the center frequency or a band width of 10 KHZ is available for each station. so when a certain instrument is producing a sound of more than the transmitter will distort this and and not a reproduction reproduction of a original signal. In FM broadcasting the modulating frequency is 75 KHZ from the center frequency. So there is no problem for reception.

INTRODUCTION:

Frequency modulation is a process in which the amplitude of the modulate carrier is kept constant,while its frequency and rate of change are varied by the modulating signal.

Broadcast band frequency modulation (FM) radio was inventedto solve existing problems with noise and fidelity on the amplitude modulation (AM) broadcast band. Thus, the FM receivers were, employing a superheterodyne converter, a wideband IF, a limiter stage, and a discriminator. Unlike the first AM radio sets, the earliest FM radio sets did not use the simplest possible methods for receiving signals. Perhaps Armstrong, the inventor of most modern radio methods, was fully aware of all the ways to receive FM.It was until much after the introduction of commercial broadcast FM that simple FM receiver designs were published or sold.

Although the title to simplicity, these radio designs are uniformly simple. These designs generally have low component counts, however the design or construction my have been far from simple.

COMPONENTS DETAILS:

SI.NO / APPARATUS REQUIRED / RANGE/TYPE / QUANTITY
1 / I C TBA 810 / _ / 1
2 / I C CXA 1619 BS / _ / 1
3 / Power connector / _ / 1
4 / Transformer / 6v-0-6v,200mA / 1
5 / Speaker / 7 ohm / 1
6 / FM tunning control variable Gang capacitor / 22PF / 1
7 / Volume control / 10 KA / 1
8 / Diode / IN 4007 / 1
9 / Inductance coils / 3 Turns,23 SWG
5 mmDiameter / 1
4Turns,23 SWG
5 mmDiameter / 1
5Turns,23 SWG
5 mmDiameter / 1
10 / Resistors / 150E,220E,330E / 1,1,2
150 Kohm / 1
100 Kohm / 1
100 ohm,2.2ohm,56ohm / Each 1
11 / Capacitors / 1000 micro farad /12V / 1
470 micro farad/16V / 1
100 micro farad/16V / 3
220 micro farad/16V / 1
0.1 micro farad / 2
0.005 micro farad / 1
0.001 micro farad / 2
4.7 pico farad / 3
0.02 micro farad / 2
22PF / 1
33 PF / 1
3.3NF / 1
100 micro farad / 1
220 micro farad/10V / 1
4.7 micro farad/1V / 1
12 / Ceramic Crystal / J10.7G MHZ / 1
13 / Ceramic Filter / L10.7 AP MHZ / 1

F.M. RECEIVER BASICS:

TYPES OF RADIO RECEIVER

Basic crystal set.
A T.R.F. Receiver.
superhetrodyne Receiver.
the Reflex Receiver.

Mainly f.m. receivers are of the superhetrodyne variety. Before we go into any depth about f.m. radio receivers let's consider the principal differences between a.m. and f.m. signals.

BACKGROUND TO FM RECEIVER DESIGN

An a.m. receiver relies upon the original carrier signal (station frequency) having been amplitude modulated. This means the original amplitude (strength) varies at an audio rate. Looking at figure 1 we can see an unmodulated carrier signal as it might be seen on an oscilloscope.

perhaps the a.m. carrier signal repeats each cycle from point (a) to point (b) in figure 2 below at the rate of 810,000 times a second, this represents a frequency of 810 Khz and would be in the a.m. radio band.
Figure 2. one complete cycle of signal If the signal were varied at 101,700,000 cycles per second then it would be 101.7 Mhz and located in the f.m. radio band.

Now if the signal of figure 1 is amplitude modulated it looks like the signal in figure 3 below.

Figure 3. - an a.m. modulated signal

In the receiver circuit a diode detector can convert that envelope above back into the original audio signal for later amplification although some distortion does result.

It was to an extent this distortion property that people sought a better means of transmission. More important it was discovered that noise (either man made QRM or natural noise QRN) was amplitude in its properties.

BLOCK DIAGRAM OF FM SUPER HETERODYNE RECEIVER

FM receivers also employs double frequency conversion.It consists of a RF stage,two frequency changer circuits(mixer and local oscillator),two IF sections,Limiter, Discriminator and amplifier stages.

RF AMPLIfIER SECTION:

It is used in front end of the FM receiver.they select desired the signal frommany modulated signals and amplify them to the required level.It is used for very important to reduce the noise figure.It is also important to match the input impedance of the receiver to that of the antenna.FM receivers are designed to operate VHF and UHF range.

FREQUENCY CHANGER:

It has two sections .i.e mixer and local oscillator.Frequency changer is also called detector circuit.By the principle of heterodyne ,input to the mixer and local oscillator output is mixed and the mixer produces the difference frequencies which is called as “Intermediate Frequency”(IF).Therefore an FM receiver employing double frequency conversion is also called as triple detection receiver.It avoids the tracking problem.

IF AMPLIFIER SECTION:

In FM the intermediate frequency and the bandwidth required are far higher than in AM broadcast receivers.Typical figures for receivers operating in the 88MHZ to 108MHZ band are an IF of 10.7 MHZ and a bandwidth of 200KHZ.The IF amplifier amplifies the intermediate frequency present at the output of the frequency changer circuit.This amplifier gives high gain and improved selectivity of the receiver.

LIMITER:

The amplified IF signals at the output of the second IF amplifier are passed through a limiter stage before being passed on to the discriminator.The purpose of a limiter stage is to provide constant amplitude IF signal with the same frequency deviation as produced by the modulating signal at the input of discriminator so that ,the amplitude variations in FM due to external and internal noises do not reach the receiver output.

DE-EMPHASIS CIRCUIT:

A de-emphasis circuit is always employed in FM receiver circuits to restore relative magnitudes of different components of AF signals as in the original modulating signal.

DISCRIMINATOR OR DETECTOR:

It converts frequency deviation to amplitude variation.FM detector usually a slope , phase discriminatoror Ratio detecter used to recover the original modulated signal.

AF and POWERAMPLIFIER:

The output of the detector is passed to an audio amplifier to amplify the detected baseband signal to the required level.Then amplified output is given to the speaker.

An oscillator is an FM detector:

An oscillator is an FM detector. If an FM signal is coupled intothe tuned circuit of an oscillator, there will be an additive effect between the FM signal and the oscillator's signal when the two match exactly in frequency. This additive effect will show up as slightly stronger oscillator signal amplitude. As the FM signal swings away from this perfectly matching frequency, the additive effect will diminish. Just like with slope detection, the amplitude variations can be used to create an audible signal. The non-linearity of most oscillators will detect the amplitude variations without the need for a diode detector.

FM STATIONS:

STATION

NAME

/ FREQUENCY RANGE
BANGALORE / 91.0 MHZ
RADIO MIRCHY / 98.3MHZ
KODAIKANAL / 100.5MHZ
KARAIKAL / 101.1MHZ
TRICHY / 102.1 MHZ
KOVAI / 103.0 MHZ
TIRUPATHY / 103.2 MHZ
GOLD / 105 MHZ
CHENNAI SURIYAN / 105.8 MHZ
COIMBATORE SURIYAN / 105.8 MHZ
TIRUNELVELI SURIYAN / 106.8 MHZ
RAINBOW / 107.1 MHZ

FM RADIO :

Supply volt=6.0v

Minimum current=10mA

Maximum current=100mA

FUNCTIONS OF IC CXA 1619 BS:

PIN NUMBERS / FUNCTIONS
1 / Ground
2 / Ground
3-Fm Disc / Phase shift circuit connected to ceramic Discriminator
4-NF / Negative Feedback
5-vol cont / Connect Variable Resistor to electronic
Volume Control
6-AM Osc / AM Local Oscillator Circuit
7-AFC / AFC Variable Capacitor
8-FM OSC / FM Local OSC Circuit
9-Reg Out / Regulator Output-1.25v
10-FM RF / Connect FM RF Tuning coil
11-AM RF IN / AM RF Input
12-NC / NO Contact
13-FM RF IN / FM RF Input
14-FE GND /

Ground

15-FM/AM FE Out / IF Output pin Of FM &AM connect IF Filter
16-FM/AM Band Select /

FM and AM Band Selection. During GND it becomes AM&FM when it Opens

17-AM IF IN /

Input Of IF AM Pin

18-FM IF IN / Input Of IF FM pin
19-NC / NO Cantact
20-Meter / For Tunning Indicator
21-IF Gnd / Ground
22,23-AFC/AGC / During AM it Determines the time constant
24-DET Out / Detection Output
25-AF IN / Power Amplifier
26-Ripple Filter / Ripple Filter
27-VCC / Power Supply Connection
28-AF Out / Power amplifier Gnd
29,30-Gnd / Ground

FUNCTIONS OF IC TBA 810:

PIN NUMBERS / FUNCTIONS / VOLT
1 / Supply / 6.0
2 / No Connection / -
3 / No Connection / -
4 / Load Resistor / 5.8
5 / Feed Back Input / 0.8
6 / Capacitor / 1.2
7 / Filter / 3.4
8 / Input Signal / 0
9 / Gnd / 0
10 / Gnd / 0
11 / No Connection / -
12 / Output Signal / 3.0

CONSTRUCTION :

In receiver circuit diagram the IC CXA 1619 BS used for FM operation and the IC TBA 810 is used as a audio frequency amplifier.

IC CXA 1619 BS is a 30 pin IC. IC TBA 810 consists of 12 pin.

In IC CXA1619 BS ,Antenna receives the station signals from the station and it is given to the pin number 13 for FM RF input. pin number 27 is used for vcc i.e 6v. The 6 v vcc is converted into 1.2v regulated output in pin number 9. pin number 1,2,4,5,12,14,19,21,29,30 are directly connected to ground. pin number 6,11,17,20,23,25,26,28 are there is no connection.FM IF output is get from pin number 15. pin number 10 gets the FM RF input . pin number 8 is used for oscillator input.

FM IF filter is a ceramic filter and it is connected to pin number 18 and feedback from pin number15.Ceramic crystal is used as a discriminater filter and it is connected to pin number 3. pin number 22 is used for FM filter,that is AFC AGC Control. AFC feedback is taken from pin number 22 to pin number7. Detector output or AF output is taken from pin number 24 and it is given to the AF amplifier through volume control.

In IC TBA 810,the AF signal from movable arm of the volume control goes to the input signal pin number 8 of the IC.The output signal is coupled to the loud speaker through coupling capacitor from pin number 12.

pin number 1 receives the power supply of 6v. pin number 5 is used for negative feedback to stablizes the AF signal. Two wings or tabs in the IC are connected to the ground. pin numbers 9&10 are go to ground. pin numbers 5,6,7 are connected to the ground through capacitor.These are called wave shaping. pin numbers 2,3,11 are no any connection.

CIRCUIT OPERATION:

The radio waves picked up by the aerial is passed on to the frequency changer or mixer-oscillator.This stage changes the incoming FMRF frequency into another intermediate radio frequency or IF . The mixer- oscillator stage will pick up the radiowave of desired station out of 100 stations coming into cantact with the aerial. This process is known as tunning.The FM RF is mixed with another wave called the oscillator RF produced by the local oscillator stage.By this process a RF signal having a different frequency called the intermediate frequency. This method is called the super heterodyne principle. The radio receivers using this method is called the super heterodyne receivers.

IF or intermediate frequency stage purpose is to tune the correct IF frequency passed on by the converter and amplify the strength of the signal. The IF or intermediate frequency used in India is between 450KHZ and 470KHZ. The common frequency selected by the manufacturer is 455KHZ.

Eventhough the frequency of the incoming RF signal is changed to a different frequency called IFRF it still contains the audio envelope which is separated by detector stage. IF wave is further rectified and filtered by filter circuits. Next the audio amplifier stage which amplifies the strength of audio the signal separated by the detector stage. After increasing the power of the audio signal it is passed on to the loud speaker which produces the sound waves.

ADVANTAGES:

1.FM is immune to noise signals and is able to reproduce all the AF frequencies.

2.Stability is very high.

3.sensitivity is also high

4. IC CXA 1619 BS Operates In both AM/FM Reception.

5.Easy to Design.

6. Bandwidth is Uniform.

7. Selectivity of the receiver is high.

APPLICATIONS:

The Radio was used in weather forecasting,entertainment,education and for military purposes.

CONCLUSION:

Thus the FM receiver was constructed using the IC CXA 1619BS and TBA 810 and it receives the station signals successfully.

On doing this project we gained more knowledge in various aspects.Now we are very clear in printed circuit board in which we can minimize the soldering work.In other conventional method the meshed wires may loose the connection and interruption.By this method we absolutely avoided it .

While purchasing the electronic components we came to know about various electronic components with the latest version and their values.We really improved our knowledge of tracing in the electronic circuits by this projects.

References:

1.Electronic Communication Systems-by KENNEDY.DAVIS

2.Communication Systems-by TAUB SCHILLING

3.Communication theory and systems-by k.SRINIVASAN

4.Basic Electronics & Radio Servicing-by KASI