AM radio help

Discussion in 'Wireless & RF Design' started by davidGG, Dec 13, 2013.

  1. davidGG

    Thread Starter Member

    Dec 22, 2012
    51
    0
    Hi.
    I'm trying to make an AM radio receiver circuit.

    So I have my antenna connected to a tank and then an envelope detector like so (sorry I forgot the resistor/capacitor in parallel after the diode)


    [​IMG]

    When I put my oscilloscope to see the output signal I see a bunch of noise. With or without the resistor/capacitor in parallel, the signal goes into the negative region, which it should not.

    Why is this? I figured that the signal must be amplified before the diode because of the forward voltage of the diode.

    Is this true? If so, do I put the amplifier in between the detector and tank circuit? Are there any good rf amplifier circuits that you can aware me of?

    Thanks for the help.
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    tap the detector down on the tank coil, this increases the voltage developed by the tank. tapping the antenna down will help too. running everything on the top of the tank coil loads the tank too much. a simple amplifier can be put in between the antenna and tank. a single mmic would work, or one transistor untuned amp.
    there are several good sites that explain these type of recievers. the crystal set socioty has a very good site with designs and design help.
    cliff
     
  3. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    Should it not be also earthed so that the diode can ditch the carrier wave?
     
  4. radiohead

    Active Member

    May 28, 2009
    474
    31
    look at this link. http://www.sci-toys.com. It has detailed instructions on how to construct an AM receiver in a few minutes. I made one and it has been zip-stripped to a telephone pole out back for over a year and still works.
     
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