DESIGN OF AM TRANSCEIVER
EXPT NO: 3(i)
To transmit a modulating signal after amplitude modulation using VCT-08 and receive the signal back after demodulating using VCT-09.
1. VCT-08 trainer kit
2. VCT-09 trainer kit
4. Patch cards
Amplitude Modulation is a process by which amplitude of the carrier signal is varied in accordance with the instantaneous value of the modulating signal, but frequency and phase of carrier wave remains constant.
The modulating and carrier signal are given by
Vm(t) = Vm sinwmt
VC(t) = VC sinwCt
The modulation index is given by, ma = Vm / VC.
Vm = Vmax – Vmin and VC = Vmax + Vmin
The amplitude of the modulated signal is given by,
VAM(t) = VC (1+ma sinwmt) sinwCt
Vm = maximum amplitude of modulating signal
VC = maximum amplitude of carrier signal
Vmax = maximum variation of AM signal
Vmin = minimum variation of AM signal
Time Period (msec)
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1. The circuit wiring is done as shown in diagram
2. A modulating signal input given to the Amplitude modulator can also be given from a external function generator or an AFO
3. If an external signal source with every low voltage level is used then this signal can be amplified using the audio amplifier before connecting to the input of the AM modulator
4. Now increase the amplitude of the modulated signal to the required level.
5. The amplitude and the time duration of the modulating signal are observed using CRO.
6. Finally the amplitude modulated output is observed from the output of amplitude modulator stage and the amplitude and time duration of the AM wave are noted down.
7. Calculate the modulation index by using the formula and verify them.
8. The final demodulated signal is viewed using an CRO at the output of audio power amplifier stage. Also the amplitude and time duration of the demodulated wave are noted down.
The modulating signal is transmitted after amplitude modulation using VCT-08 and the signal is received back after demodulation using VCT-09