Amplitude Modulator and Demodulator Trainer Kit

•Modulation is the process of varying one or more properties of a periodic waveform (carrier signal) with a modulating signal (information) to be transmitted.

•A modulator is a device that performs modulation.

•A demodulator is a device that performs demodulation, the inverse of modulation.

•In AM, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted.

•That waveform may, for instance, correspond to the sounds to be reproduced by a speaker, or the light intensity of television pixels.

Things that are required:-

For AM Modulator :-

1.1N4148 Diode

2.Resistor : 2.2K (2pcs)

3.Inductor : 10 µH

4.Trimmer : 3-40 pF

For AM Demodulator :-

1.1N34 Diode

2.Resistor : 10K

3.Capacitor : 10nF

Others:-

Box : 6”x8”

Banana Socket : Red-Black (5 pairs)

Step 1: Modulator Overview

Modulation is a process generally used for radiating the low frequency audio signals for longer distances. Here the low frequency audio signal is superimposed with the high frequency carrier wave.The amplitude modulation is that where the amplitude of high frequency carrier wave is changed accordance with the intensity of the signal but the frequency of the modulated wave will be the same.

Step 2: How to Make Modulator Circuit

This simple diode modulator delivers excellent results when used for high percentage modulation at low signal levels. Constants are shown for a carrier frequency of about 10 MHz, but, with a suitable tank, the circuit will give good results at any frequency at which the diode approximates a good switch. To extend frequency above that for which the IN4148 is suited, a hot-carrier diode (HP2800, etc.) can be substituted.

A shunt resistor across the tank circuit can be used to reduce the circuit Q so as to permit high percentage modulation without appreciable distortion.

Step 3: Demodulator Overview

Recovering the original message from a modulated carrier is called demodulation and this is the main purpose of communications and telecommunications receivers. The circuit that is widely used to demodulate AM signals is called an envelope detector.

As you can see, the rectifier stage chops the AM signal in half letting only one of its envelopes through the upper envelope in this case but the lower envelope is just as good. This signal is fed to an RC LPF which tracks the peaks of its input. When the input to the RC LPF is a rectified AM signal, it tracks the signal's envelope. Importantly, as the envelope is the same shape as the message, the RC LPF's output voltage is also the same shape as the message and so the AM signal is demodulated.

Step 4: How to Make Demodulator Circuit

Envelope detector circuit uses a diode, a capacitor and a resistor and it is just like a half wave rectifier followed by a low-pass filter. It is a linear detector which takes high frequency RF signal as input and gives an output which is the envelope of the input signal. A diode detector is a type of envelope detector and is used for the detection of AM signal.

Here the input signal is rectified by the series diode D. The combination of capacitor C and resistor R behaves like a low-pass filter. The input signal contains both the original message and the carrier wave where the capacitor helps in filtering out the RF carrier waves. The capacitor gets charged during the rising edge and discharges through the resistor R in falling edge. Thus the capacitor helps in giving an envelope of the input as output.

Step 5: The Trainer Kit

The final kit is here.The drill machine can be used to create holes according to banana sockets size and tightly fitted with nuts so that patch cords can be adjusted.