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.

 

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

 

Only caveat would be if there was some DC offset on the output of the RF amp. Otherwise, makes no difference.

 

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.

 

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.

Hi,

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

 

Hi,

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

There are cascaded op amps before the diode.

 

There are cascaded op amps before the diode.

Hi,

What kind of op amps and what is the expected frequency of reception? (like 1MHz for example)

 

Hi,

What kind of op amps and what is the expected frequency of reception? (like 1MHz for example)

Their gbwp were 4 MHz.

 

Their gbwp were 4 MHz.

Hi,

Ok great, so what frequency are you trying to receive or maybe the whole AM band?

 

Hi,

Ok great, so what frequency are you trying to receive or maybe the whole AM band?

Tuner was designed to pass only 175 kHz signal.

 

Tuner was designed to pass only 175 kHz signal.

Hi,

Ok. Well then 4MHz op amps have to have reduced gain so they can pass that signal with enough amplitude to drive the next stage properly.

 

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.

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.