What does happen if the direction of the diode used for AM demodulation is reversed?

Thread Starter

SimpleKCLSimpleKVL

Joined Mar 3, 2019
11
Hello,

In the lab, I built the basic radio receiver circuit that you can see in the attachment, and I used the germanium diode for the demodulation. Fortunately, it worked properly but I wonder that what happens if we change its direction ? Can we get sound from the headphone ?


Thank you in advance.

Note: After I built the circuit, I forgot testing its direction's effect so please don't ask me why didn't you try it. :D
 

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bertus

Joined Apr 5, 2008
20,461
Hello,

In the given picture, the negative tops of the signal are detected.
The capacitor Cb will remove the DC part and the amplifier will work fine.
When the diode is reversed, the positive tops of the signal are detected.
The capacitor Cb will remove the DC part again and teh amplifier will also work fine.

Bertus
 

Thread Starter

SimpleKCLSimpleKVL

Joined Mar 3, 2019
11
So if I understand correctly, you mean the cb capacitor blocks any dc off set (negative or positive) and we get the same signal at the output. Thanks for your rapid answers.
 

MrAl

Joined Jun 17, 2014
7,508
Hello,

In the lab, I built the basic radio receiver circuit that you can see in the attachment, and I used the germanium diode for the demodulation. Fortunately, it worked properly but I wonder that what happens if we change its direction ? Can we get sound from the headphone ?


Thank you in advance.

Note: After I built the circuit, I forgot testing its direction's effect so please don't ask me why didn't you try it. :D
Hi,

What are you using for the "Amp" triangle block just before the diode?
 

Ramussons

Joined May 3, 2013
814
Hello,

In the lab, I built the basic radio receiver circuit that you can see in the attachment, and I used the germanium diode for the demodulation. Fortunately, it worked properly but I wonder that what happens if we change its direction ? Can we get sound from the headphone ?


Thank you in advance.

Note: After I built the circuit, I forgot testing its direction's effect so please don't ask me why didn't you try it. :D
In this circuit, it makes no difference.
But in commercial receivers, the DC derived after the diode (called detection) is used as an Automatic Gain Control (AGC) voltage on the preceding amps, normally at IF stage. In such circuits, reversing the diode will make a big difference.
 
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