Study of FM modulation and demodulation (Transmitter and Receiver) & Calculation of parameters

Aim

Study of FM modulation and demodulation (Transmitter and Receiver) & Calculation of parameters.

(a) To generate frequency modulated signal and determine the modulation index and Bandwidth.

Apparatus Required:

1. Frequency Modulation and Demodulation Trainer
2. Function Generator
3. Oscilloscope
4. Connecting Wires

Theory

The process, in which the frequency of the carrier is varied in accordance with the Instantaneous amplitude of the modulating signal is called “Frequency Modulation”. The FM signal is expressed as where Ac is amplitude of the carrier signal; f c is the carrier frequency β is the modulation index of the FM wave

Procedure:-

1. Switch on the FM experimental board.
2. Connect Oscilloscope to the FM O/P and observe that carrier frequency at that point without any A.F. input.
3. Connect around 7KHz sine wave (A.F. signal) to the input of the frequency modulator (At AF input).
4. Now observe the frequency modulation output on the 1st channel of on CRO and adjust the amplitude of the AF signal to get clear frequency modulated wave form.
5. Vary the modulating frequency (A.F Signal) and amplitude and observe the effects on the modulated waveform.

Precautions:

1. Connect the circuit properly.
2. Apply the required voltages wherever needed.
3. Do not apply stress on the components.

Result:Frequency of the Carrier signal varied according to the baseband signal and waveform observed.

(b) To Demodulate a Frequency Modulated signal using FM detector.

Apparatus Required:

1. Amplitude Modulation and Demodulation Trainer
2. Function Generator
3. Oscilloscope
4. Connecting Wires

Theory

Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave.

There are many types of modulation so there are many types of demodulators. The signal output from a demodulator may represent sound (an analog audio signal), images (an analog video signal) or binary data (a digital signal).

The process, in which the frequency of the carrier is varied in accordance with the Instantaneous amplitude of the modulating signal is called “Frequency Modulation”. The FM signal is expressed as where Ac is amplitude of the carrier signal; f c is the carrier frequency β is the modulation index of the FM wave.

In FM demodulation process we extract message signal from the FM modulated signal

Procedure:-

1. Switch on the FM experimental board.
2. Connect Oscilloscope to the FM O/P and observe that carrier frequency at that point without any A.F. input.
3. Connect around 7KHz sine wave (A.F. signal) to the input of the frequency modulator (At AF input).
4. Now observe the frequency modulation output on the 1st channel of on CRO and adjust the amplitude of the AF signal to get clear frequency modulated wave form.
5. Vary the modulating frequency (A.F Signal) and amplitude and observe the effects on the modulated waveform.
6. Connect the FM o/p to the FM i/p of De-modulator.
7. Vary the potentiometer provided in the demodulator section.
8. Observe the output at demodulation o/p on second channel of CRO.
9. Draw the demodulated wave form

Precautions:

1. Connect the circuit properly.
2. Apply the required voltages wherever needed.
3. Do not apply stress on the components.

Result:Original baseband signal recovered from Frequency modulated wave.