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Please check if this circuit can act as AM generator (for lab demo)

  1. Dec 20, 2012 #1
    Hi PF,
    I have a transistor circuit with me with IFT . Please see that if this circuit can be used for AM generation. Also please suggest the design procedure and working of circuit. Please point out any errors in the circuit. I don't know if I have to supply separate carrier signal(I assume 455KHz is the carrier signal generated from tuned IFT). I am attaching the circuit.



    -Devanand T

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  2. jcsd
  3. Dec 20, 2012 #2


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    Yes, it could generate AM. Not very good, though.

    You would just pass the wire going to +12V through the secondary of a transformer.
    Apply audio to the primary of the transformer.

    There are two problems.

    The output will also contain frequency modulation, so it may sound distorted.

    The output will be on 455 KHz and most receivers don't work on that frequency.

    Inside 455 kHz IF transformers there is a capacitor which can be replaced with a smaller one to bring the resonant frequency up into the AM broadcast band.
  4. Dec 20, 2012 #3
    Is this an oscillator? Oscillators should not be amplitude-modulated, or you risk to block them.

    [Or if it's a neutrodyned amplifier, you should consider something less old...]

    Modulate the amplitude on a subsequent stage. Better: since intermediate stages have no linear behaviour, AM is done at the very last stage normally. And for linearity, modulation is done by the supplied power, at the collector - not a the base.
    Last edited: Dec 20, 2012
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