When I first built AM receiver, my first stage of amplifier was a common base and it was also demodulating?

Question

when I first built AM receiver, my first stage of amplifier was a common base and it was also demodulating. but when i built the circuit again using slightly different components (mostly resistors). At common base stage(first stage), there was no demodulation and second stage (common emitter) amplifier was demodulating. Can somebody explain why?

Answer 1

Demodulation of an AM signal will not occur in a normal amplifier, you must have had the CB stage biased incorrectly. Now you have it biased in a more linear region and it is not demodulating. But now your CE stage is also biased incorrectly and is demodulating, or possibly you are overdriving it.

Just put a diode before the first stage! Either series or shunt. That will do the demodulation for you. Use a small signal diode that has a high speed rating.  Or if you have a good small signal transistor, just use the EB junction of that.