SIGMA

FREQUENCY MODULATION TRANSMITTER TRAINER &

FREQUENCY DEMODULATION RECEIVER TRAINER

MODEL - COM311 & COM312

Mfd.by: - SIGMA TRAINERS E-103, Jai Ambe Nagar, Near Udgam School, Thaltej, AHMEDABAD - 380054. Phone : +91-79-26852427 /26850829 Fax : +91-79-26840290 Email : sales@sigmatrainers.com : sigmatrainers@sify.com Web : www.sigmatrainers.com

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INTRODUCTION This trainer has been designed with a view to provide practical and experimental knowledge of Frequency

Modulation Transmitter & Demodulation Receiver technique on a SINGLE P.C.B

TRANSMITTER SECTION

SPECTIFICATIONS

1. Power supply requirement : 230V AC, 50 Hz.

2. Built in IC based power supply : +12V, -12V

3. Synchronous Function Generator

Frequency Range : 100 Hz to 1 KHz

1K Hz to 10 KHz

Amplitude : 0 to 2Vp-p

4. FM Modulators : Varactor FM Modulator

Reactance (PM) Modulator

Central Frequency : 455KHz.

5. Frequency Converter (Mixer)

6. Standard Accessories : 1. Experimental and Circuit Description Manual.

2. Connecting Patch cords. (6 Nos.)

EXPERIMENTS 1. Study of Varactor Modulator and Reactance Modulator

2. To generate FM signal using Varactor Modulation

3. To generate FM signal using Reactance Modulation

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RECEIVER SECTION

SPECTIFICATIONS

1. Power supply requirement : 230V AC, 50 Hz.

2. Built in IC based power supply : +12V, -12V

3. Synchronous Function Generator

Frequency Range : 100 Hz to 1 KHz

1K Hz to 10 KHz

Amplitude : 0 to 2Vp-p

4. FM Demodulator : Detuned Resonant Detector

Quadrature Detector

Foster-Seeley Detector

Ratio Detector

Phase Locked Loop Detector

5. FM Demodulator Central Frequency : 455KHz.

6. Low pass Filter : 3.4 KHz, Cut off frequency

7. Amplitude Limiter : 1 no.

8. Standard Accessories : 1. Experimental and Circuit Description Manual.

2. Connecting Patch cords. (6 Nos.)

EXPERIMENTS 1. Study of FM Demodulators.

Detuned Resonant Detector

Quadrature Detector

Foster-Seeley Detector

Ratio Detector

Phase Locked Loop Detector

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CHAPTER-1

THEORY OF FREQUENCY MODULATION

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the sine waves signals.

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CHAPTER-2

THEORY OF FREQUENCY DEMODULATION

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PHASE DETECTOR

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CHAPTER-3

EXPERIMENT-1

FM Generation Using Reactance Modulator and FM demodulation using PLL

(See connection diagram CN1)

1. Connect links as shown in connection diagram CN1.

2. Select waveform switch to Sine position in Function generator section. Connect CRO channel -1 at Sine

O/P terminal TP1. Trigger CRO by channel-1.

Adjust amplitude of sine wave to 1Vpp and audio frequency to 1 KHz. ______Waveform (W1)

+ 0.5V

3 Now set amplitude of sinewave to zero. Connect CRO channel -2 output of Reactance modulator at FM

O/P TP6 terminal. Trigger CRO by Channel-2. It will be 5Vpp, 455 KHz sine wave. This is FM carr ier

signal.

_______Waveform (W2)

+2V

-2V 455KHz

4. Now change amplitude of sine wave to 1 Vpp as previous and observe Frequency Modulated waveform at

output of Reactance modulator TP6 terminal. _______Waveform (W3)

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5. Connect FM modulated output TP6 to I/P of Amplitude limiter section in FM receiver trainer at terminal

TP1. Observe fix amplitude FM modulated signal at the output of Amplitude Limiter TP2.

6. Connect FM modulated output TP2 of Amplitude limiter to the input of PLL detector at TP3.

Connect o/p of PLL TP4 to the input of Low Pass filter TP5. Keep VCO switch in PLL detector to ON

position.

7. Now observe output of low pass filter TP6. It will be demodulated audio signal. If signal is not proper

vary center frequency of Reactance modulator. _______Waveform (W4)

8. See the effect on the FM modulated signal by varying the Audio Oscillator Frequency & Amplitude.

9. Vary R.F. carr iers Oscillator Frequency by Frequency pot (It varies from 453KHz to 457KHz) and

observe its effect on the FM modulated signal

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EXPERIMENT-2

Fm Voice Modulation and demodulation

(See connection diagram CN2)

1. Connect links using patch cords as per connection diagram CN2.

2. Connect Microphone at Microphone socket in FM transmitter trainer .

Connect Loudspeaker at Loudspeaker socket in FM receiver trainer .

3. Keep volume controls of audio Pre-amplifier and output audio amplifier in mid position.

4. Speak to mike and hear recovered audio in LS of output audio amplifier .

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EXPERIMENT- 3

FM Generation Using Varactor Modulator and FM demodulation using Quadrature Detector (See connection diagram CN3)

1. Connect links as shown in connection diagram CN3.

2. Select waveform switch to Sine position in Function generator section. Connect CRO channel -1 at Sine

O/P terminal TP1. Trigger CRO by channel-1.

Adjust amplitude of sine wave to 1Vpp and audio frequency to 1 KHz. ______Waveform (W1)

+ 0.5V

3 Now set amplitude of sinewave to zero. Connect CRO channel -2 output of Varactor modulator at FM O/P

TP9 terminal. Trigger CRO by Channel-2. It will be 5Vpp, 455 KHz sine wave. This is FM carr ier signal.

_______Waveform (W2)

+2V

-2V 455KHz

4. Now change amplitude of sine wave to 1 Vpp as previous and observe Frequency Modulated waveform at

output of Varactor modulator TP9 terminal. _______Waveform (W3)

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5. Connect FM modulated output TP6 to I/P of Amplitude limiter section in FM receiver trainer at terminal

TP1. Observe fix amplitude FM modulated signal at the output of Amplitude Limiter TP2.

6. Connect FM modulated output TP2 of Amplitude limiter to the input of Quadrature detector .

Connect o/p of quadrature detector TP8 to the input of Low Pass filter TP5. Keep VCO switch in PLL

detector to OFF position.

7. Now observe output of low pass filter TP6. It will be demodulated audio signal. If signal is not proper

vary center frequency of Reactance modulator. _______Waveform (W4)

8. See the effect on the FM modulated signal by varying the Audio Oscillator Frequency & Amplitude.

9. Vary R.F. carr iers Oscillator Frequency by Frequency pot (It varies from 453KHz to 457KHz) and obs erve

its effect on the FM modulated signal

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EXPERIMENT-4

FM Generation Using Reactance Modulator and FM demodulation using Phase Detector

(See connection diagram CN4)

1. Connect links as shown in connection diagram CN4.

2. Select waveform switch to Sine position in Funct ion generator section. Connect CRO channel -1 at Sine

O/P terminal TP1. Trigger CRO by channel-1.

Adjust amplitude of sine wave to 1Vpp and audio frequency to 1 KHz. ______Waveform (W1)

+ 0.5V

3 Now set amplitude of sinewave to zero. Connect CRO channel -2 output of Reactance modulator at FM

O/P TP6 terminal. Trigger CRO by Channel-2. It will be 5Vpp, 455 KHz sine wave. This is FM carr ier

signal.

_______Waveform (W2)

+2V

-2V 455KHz

4. Now change amplitude of sine wave to 1 Vpp as previous and observe Frequency Modulated waveform at

output of Reactance modulator TP6 terminal. _______Waveform (W3)

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5. Connect FM modulated output TP6 to I/P of Amplitude limiter section in FM receiver trainer at terminal

TP1. Observe fix amplitude FM modulated signal at the output of Amplitude Limiter TP2.

6. Connect FM modulated output TP2 of Amplitude limiter to the input of Phase detector at TP9.

Connect o/p of Phase detector TP10 to the input of Low Pass filter TP5. Keep VCO switch in PLL

detector to OFF position.

7. Now observe output of low pass filter TP6. It will be demodulated audio signal. If signal is not proper

vary center frequency of Reactance modulator. _______Waveform (W4)

8. See the effect on the FM modulated signal by varying the Audio Oscillator Frequency & Amplitude.

9. Vary R.F. carr iers Oscillator Frequency by Frequency pot (It varies from 453KHz to 457KHz) and

observe its effect on the FM modulated signal

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EXPERIMENT-5

FM Generation Using Varactor Modulator and FM demodulation using Foster-Seeley Detector (See connection diagram CN5)

1. Connect links as shown in connection diagram CN5. Keep selector switch in Ratio detector section at “S”

postion.

2. Select waveform switch to Sine position in Function generator section. Connect CRO channel -1 at Sine

O/P terminal TP1. Trigger CRO by channel-1.

Adjust amplitude of sine wave to 1Vpp and audio frequency to 1 KHz. ______Waveform (W1)

+ 0.5V

3 Now set amplitude of sinewave to zero. Connect CRO channel -2 output of Varactor modulator at FM O/P

TP9 terminal. Trigger CRO by Channel-2. It will be 5Vpp, 455 KHz sine wave. This is FM carr ier signal.

_______Waveform (W2)

+2V

-2V 455KHz

4. Now change amplitude of sine wave to 1 Vpp as previous and observe Frequency Modulated waveform at

output of Varactor modulator TP9 terminal. _______Waveform (W3)

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5. Connect FM modulated output TP6 to I/P of Amplitude limiter section in FM receiver trainer at terminal

TP1. Observe fix amplitude FM modulated signal at the output of Amplitude Limiter TP2.

6. Connect FM modulated output TP2 of Amplitude limiter to the input of Foster Seeley detector at TP11.

Connect o/p of Foster Seeley detector TP12 to the input of Low Pass filter TP5. Keep VCO switch in PLL

detector to OFF position.

7. Now observe output of low pass filter TP6. It will be demodulated audio signal. If signal is not proper

vary center frequency of varactor modulator . _______Waveform (W4)

8. See the effect on the FM modulated signal by varying the Audio Oscillator Frequency & Amplitude.

9. Vary R.F. carr iers Oscillator Frequency by Frequency pot (It varies from 453KHz to 457KHz) and obs erve

its effect on the FM modulated signal

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EXPERIMENT-6

FM Generation Using Varactor Modulator and FM demodulation using Ratio Detector (See connection diagram CN6)

1. Connect links as shown in connection diagram CN6. Keep selector switch in Ratio detector section at “R”

position.

2. Select waveform switch to Sine position in Function generator section. Connect CRO channel -1 at Sine

O/P terminal TP1. Trigger CRO by channel-1.

Adjust amplitude of sine wave to 1Vpp and audio frequency to 1 KHz. ______Waveform (W1)

+ 0.5V

3 Now set amplitude of sinewave to zero. Connect CRO channel -2 output of Varactor modulator at FM O/P

TP9 terminal. Trigger CRO by Channel-2. It will be 5Vpp, 455 KHz sine wave. This is FM carr ier signal.

_______Waveform (W2)

+2V

-2V 455KHz

4. Now change amplitude of sine wave to 1 Vpp as previous and observe Frequency Modulated waveform at

output of Varactor modulator TP9 terminal. _______Waveform (W3)

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5. Connect FM modulated output TP6 to I/P of Amplitude limiter section in FM receiver trainer at terminal

TP1. Observe fix amplitude FM modulated signal at the output of Amplitude Limiter TP2.

6. Connect FM modulated output TP2 of Amplitude limiter to the input of Ratio detector at TP11.

Connect o/p of Ratio detector TP13 to the input of Low Pass filter TP5.

7. Now observe output of low pass filter TP6. It will be demodulated audio signal. If signal is not proper

vary center frequency of Varactor modulator . _______Waveform (W4)

8. See the effect on the FM modulated signal by varying the Audio Oscillator Frequency & Amplitude.

10. Vary R.F. carr iers Oscillator Frequency by Frequency pot (It varies from 453KHz to 457KHz) and obs erve

its effect on the FM modulated signal

-1V

7. See the effect on the FM demodulated signal by varying the Audio Oscillator Frequency and Amplitude.

Also hear different tones from loudspeaker.

8. Vary R.F. carr ier Oscillator Frequency and observe its effect on the FM demodulated signal.

Conclusion: -

The frequency demodulation process observed.

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CHAPTER-4

TEST POINTS

TRANSMITTER SECTION

T01 : Sine wave O/P

T02 : GND

T03 : Mixer I/P

T04 : Mixer O/P

T05 : GND

T06 : FM Reactance O/P

T07 : Sin wave I/P

T08 : Amplified I/P

T09 : FM Varactor O/P

T10 : Sin wave I/P

T11 : +12V

T12 : -12V

TEST POINTS

RECEIVER SECTION

T01 : FM I/P

T02 : Limiter O/P

T03 : Limiter I/P

T04 : PLL Detector O/P

T05 : Detected I/P

T06 : Filtered O/P

T07 : GND

T08 : Quadrature Detector O/P

T09 : Limiter I/P

T10 : Phase Detector O/P

T11 : Limiter I/P

T12 : F.S. Detector O/P

T13 : Ratio Detector O/P

T14 : +12V

T15 : -12V

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