Amplitude Modulator Circuit not working

Thread Starter

DD Ki Vines

Joined Apr 20, 2019
12
Today I built a amplitude modulator circuit and I think that the circuit is working but not in the way it should work,the lower envelope of the AM wave is getting shifted to the right resulting in such a waveform,I really can't understand what the problem is or even it's a problem or not(because the upper envelope of the AM wave is not affected)and if it's a problem then what the solution is....someone please help me

This is the waveform that I got the wave below in pink color is message(18KHz) and carrier is 220KHz sine wave
DSO00029.jpeg
The circuit diagram is
transistor used in circuit is 2n3904
IMG_20200325_191318_1.jpg
 

crutschow

Joined Mar 14, 2008
25,465
Your circuit is adding the two signal amplitudes together, not multiplying them, as is required for AM.
You need the circuit to change the amplitude of the carrier is response to the modulating signal.
 
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Thread Starter

DD Ki Vines

Joined Apr 20, 2019
12
Your circuit is adding the two signal amplitudes together, not multiplying them, as is required for AM modulation.
so sir is it ok or not?....i mean whatever my circuit is producing can that be called AM?....or if this signal is transmitted can the receiver produce the original signal....??? and last but not the least sir,can u share a easy to build simple AM modulator circuit which can be fabricated on breadboard....???
 

crutschow

Joined Mar 14, 2008
25,465
is it ok or not?....i mean whatever my circuit is producing can that be called AM?....or if this signal is transmitted can the receiver produce the original signal....?
Not, No, and No.

This is what AM modulation looks like.
See the difference between this and your waveform?

1585165333814.png

Here are some examples of AM modulator circuits.
I'll leave you to pick the best one for your needs.
 

Ramussons

Joined May 3, 2013
871
What is that MOSFET supposed to do? Where is the supply for it to work?
If you are using it as just a diode, use a transformer coupling for the output and you will get a low level AM signal.
 

Audioguru again

Joined Oct 21, 2019
1,938
Your Mosfet body diode will rectify the high frequency signal when the modulation signal is +0.7V and higher, then the Mosfet will do nothing until the modulation signal is -5V or less when it will turn on and reduce the high frequency signal level. Not what you want.
 
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