Amplitude Modulation Hardware Issue

Thread Starter

guptamridul477

Joined Apr 28, 2024
13
Hey Community
As a part of a project, I am building an Amplitude Modulator and synchronous demodulator on breadboard. For that, I first simulate a circuit on LTSpice. The circuit and modulated output is shown in the image below. The issue is that the complete sinusoidal signal is not getting modulated. when you zoom the modulated signal, you see that two waves are located with a distance between them. How can I correctly modulate the signal? The reference images and the LTSpice model are attached alongside. Thanks in advance for the help.
1714318582514.png1714318613785.png
 

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Thread Starter

guptamridul477

Joined Apr 28, 2024
13
Ahhhh...........silly mistake no 1.
I actually took the reference from this YT video -
. Yes the point is connected. The RF input is the carrier signal.
But now after connecting, the result is even more worse. I have attached the pics. Why is there a spike in the modulated signal. Which value is letting this happen. Actually, I need to demonstrate this for an audio signal. (Taking sine wave is just for test). Can you please suggest me the changes I should make to this circuit in order to get a perfectly modulated signal atleast for sine wave. Thanks in advance.
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Thread Starter

guptamridul477

Joined Apr 28, 2024
13
Actually, I don't have all values of capacitances and resistances available for hardware model. So, I had to change parameters according to the values I had. I made my circuit through hit-and-trial method i.e checking by increasing and decreasing values since I don't know the exact calculation behind the values. Can you please tell me how to calculate which values to take and how to change the parameters? I know this is a very tedious task to write so much just to explain me but I request you because I am unable to find how to do so on the internet.
A very sincere thanks in advance
 

Thread Starter

guptamridul477

Joined Apr 28, 2024
13
Its just a project of Hardware demonstration of Amplitude Modulation for audio wave(maybe a song) as an input signal and take its output. What do you want to know by specification?
 

Thread Starter

guptamridul477

Joined Apr 28, 2024
13
Thanks for it. But the circuit you provided does not work well for audio file. Also, can u tell me how did you determine the resistor and capacitor values used in the circuit. the audio file (test2.wav (zipped)) is attached along.
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ericgibbs

Joined Jan 29, 2010
19,091
Hi gup,
The amplitude of your wav audio signal is much too low, it has to be amplified by a factor of ~7000 in order to modulate the carrier signal correctly.
E
Note, I have edited your wav file name.


Update: I have just noticed that the Modulated carrier signal is the inverse of the
audio modulating signal! See 2nd Image.
If you look at approx 2.1 mSec in the plot you can see the maximum carrier and audio are inverted.
@crutschow will advise.
EG57_ 1692.png

EG57_ 1691.png
 

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Last edited:

Thread Starter

guptamridul477

Joined Apr 28, 2024
13
I don't have hardware amplifier. Also, when I checked the peak-to-peak voltage of audio signal through laptop is able to reach max of 0.2mV. What should be the changes I can do in my circuit design to properly modulate the audio signal? Also, the frequency of that sound is around 11kHz. Please suggest the changes for the same as well.
Thanks in advance
 
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