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FM modulator

Discussion in 'Electronic Design' started by thoppay, Nov 7, 2005.

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  1. thoppay

    thoppay Guest

    Could anyone help me in designing a FM modulator with varactor diodes
    and a signal generator.

  2. If you have an old trans. radio with AFC you simply cut the AFC circuit
    anf instad of the control voltage you can put in Audio signals.

    A sine osc. I assume is available.
  3. Phil Allison

    Phil Allison Guest

    ** NOTICE :

    We have another " gmail" & GG poster with a funny name.

    As such, he is to be automatically treated as a hostile invader / troll .

    ** You cannot externally alter the output frequency of a signal generator.

    Now come back and post a reply that demonstrates you are not a fuckwit and
    not a troll.

    .......... Phil
  4. I thought this group was unmoderated? If the OP has a "design" question
    and it's not homework, I would be happy to help.

    BTW, I like GG.

    Frank Raffaeli
  5. Phil Allison

    Phil Allison Guest

    "Frank Raffaeli"<

    ** I see you like to beg the question.

    ** Your secret is safe with me.

    ............. Phil
  6. troll .

    If you say it's so Phil, it really must be true. yaaawwwwnnnnnn
    That's funny because the el-cheapo POS that I have has a sweep input. I
    didn't get it from DSE, so maybe that's why it's so fancy. ;-)
  7. Phil Allison

    Phil Allison Guest

    "Anthony Fremont"

    ** Wot - to cold for you to troll the public conveniences today ?

    ........... Phil
  8. Amazing what your selective trimming can do for the meaning of my post
    .... ;-)

    What's your gripe with the gmail folks with a funny name? I assume you
    believe they're all after high-tech secrets, etc.

    Your presumptions may outweigh you.

    Frank Raffaeli
  9. Phil Allison

    Phil Allison Guest

    "Frank Raffaeli"

    ** Yours are like a mill stone necklace right now.

    ......... Phil
  10. Where is my post Phil? As usual you have snipped away the context. If
    you'd like to debate with me, I'd appreciate it if you'd keep to the
    subject at hand even when you know that you're wrong. What about the
    sweep input Phil, couldn't the OP use that to FM the output signal?
    Waiting with bells on......
  11. My apologies to the OP, for the diversion. If you need a VCO circuit,
    you need to specify the constraints. As for the FM modulation part -
    same story. Here is one that will do -120 dBc from 55MHz to 110 MHz:

    There are a couple layout quirks, so write me before impementing it.

    To the wordsmith troll and self-appointed moderator: should you have a
    genuine contribution to this thread regarding VCO's, now would be the
    opportune time to produce it.

    Frank Raffaeli
  12. John Larkin

    John Larkin Guest

    Actually, you can. It's called the "phasing method" of generating FM.

  13. Phil Hobbs

    Phil Hobbs Guest

    Audience note:
    A nice piece of artistic indirection--Phil is trying to get us to believe
    that the *other* guy is the troll. Note however that he always makes his
    entrance from under the stone bridge in the left background of the scene.

    We now return you to our normal programming.


    Phil Hobbs
  14. SioL

    SioL Guest

    Indeed, but not in a wideband manner, which is probably what he wants.
    Not without multiplying it 9 or more times at least afterwards.
  15. John Larkin

    John Larkin Guest

    The (vanished?) OP didn't specify. But with enough phase-shift

    And there are other ways to FM a fixed-frequency input.

  16. ">>
    Where did the magic number 9 come from, especially without specifying the

    Say, for example, a phase locked loop with the filter time constant chosen
    so as to not pass audio signals.

  17. John  Larkin

    John Larkin Guest

    Right, that's one.

    Anybody want to contribute others?

  18. Phil Hobbs

    Phil Hobbs Guest

    A motorized trombone line;

    A cascade of varactor-tuned 0/pi phase shifters (the ones with the +-1
    gain amplifier and the RC lowpass on the + input, or the ones with a
    quadrature hybrid);

    SSB mix with a high frequency tunable oscillator, run the results
    through a fixed delay, and mix back down again;

    running it through a CCD delay line with a variable clock frequency;

    Or even recording on reel-to-reel tape it and slowing the takeup reel
    with your thumb.


    Phil Hobbs
  19. Phil Hobbs

    Phil Hobbs Guest

    Uurgh, haven't had my coffee this morning. Should have read, "Or even
    recording it on reel-to-reel tape and slowing the takeup reel with your


    Phil Hobbs
  20. Rich Grise

    Rich Grise Guest

    6V lantern battery, a 555, and a carbon mic. ;-)

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