AM demodulator circuit

Discussion in 'General Electronics Chat' started by Hariosagpat, Sep 9, 2007.

  1. Hariosagpat

    Thread Starter New Member

    Sep 6, 2007
    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:

  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    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.
  3. SgtWookie


    Jul 17, 2007
    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.

    Yes, that creates a resonant "tank" LC circuit, which will be most sensitive to one particular frequency.
    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 ;)
  4. Hariosagpat

    Thread Starter New Member

    Sep 6, 2007
    Thanks guys :)