How AM modulation circuit works | applied electronics engineering

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How AM modulation circuit works

By Applied Electronics - Friday, January 6, 2017 No Comments
Here we explain how AM modulation circuit works. The circuit diagram is shown below. In the circuit shown, the two signals, one 500Hz(within the frequency range of speech) and a 500KHz of the desired carrier signal is to be mixed and sent to the antenna.

Conceptual AM Modulation Circuit Diagram
Conceptual AM Modulation Circuit Diagram

The audio signal is supposed to be amplified by a audio amplifier first. Then secondly the amplified audio signal is coupled by the lower transformer and enters the LC tank where the mixing takes place with the carrier signal. This process of audio signal flow in the circuit is shown by the picture below-

audio signal flow in am modulation circuit
audio signal flow in am modulation circuit


The upper part is a Tuned RF Amplifier-

tuned RF amplifier
tuned RF amplifier

Now the carrier signal flow into the tuned RF circuit is shown below-

carrier signal flow in am circuit
carrier signal flow in am circuit
The mixing between the audio signal and the carrier signal takes place in the LC tank and the mixed signal ultimately passes into the antenna.

mixing of signal in am circuit
mixing of signal in am circuit
This is how AM circuit works. In this example no IC or special purpose mixer and amplifier have been used. This is a DIY AM circuit which you can build at home. A more simpler circuit without tank circuit and just using single transistor is shown in ASK modulation with Proteus Professional Software.

If you want to know how AM radio works using IC then see the AM circuit using AD633 multiplier and simulation in proteus post. For book you can read RF Circuit Design PDF download free.

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