AM demodulator circuit

Thread Starter

Hariosagpat

Joined Sep 6, 2007
2
Hi guys,

This is the circuit:


Now my question is if i am to build that circuit, i have to take a transformer, connect one end of the primary winding to the antenna and ground the other end????? Where do i ground it ???? Do i connect the variable capacitor to the secondary of the transformer??? And is that L1 the inductance of the secondary of the transformer ? :confused:

Thanks
 

Ron H

Joined Apr 14, 2005
7,014
That's the schematic of a simple crystal radio. Do a search for "crystal radio" or "crystal set". You will find a huge amount of information.
 

SgtWookie

Joined Jul 17, 2007
22,220
Hi guys,

This is the circuit:


Now my question is if i am to build that circuit, i have to take a transformer, connect one end of the primary winding to the antenna and ground the other end????? Where do i ground it ????
It needs to have a signal ground, otherwise there will be no path for the RF current. You could use the ground on a wall outlet. Or even just a chunk of metal. Or you could just hold that wire in your hand. It doesn't necessarily need earth ground, but it does need somewhere to get electrons from/send electrons to.

Do i connect the variable capacitor to the secondary of the transformer???
Yes, that creates a resonant "tank" LC circuit, which will be most sensitive to one particular frequency.
And is that L1 the inductance of the secondary of the transformer ?
That's correct. The transformer is not only being used as an "impedance match" for the antenna, but the secondary winding is being used as a resonant LC tank circuit.

It's a classic crystal set, as Ron H already mentioned. My grandfather made one of those around 1907 when he was growing up in NYC. I made one as a kid, too.

They still work - no batteries needed ;)
 
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