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transform GHz to MHz so I can use my Oscope

Discussion in 'Electronic Basics' started by jw, Sep 1, 2005.

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  1. jw

    jw Guest


    I have an oscope that can operate at up to 100 MHz.

    My situation is that I want to measure the voltage magnitude of a signal
    that could have a frequency up to 1GHz, this is not a square wave shape, it
    is probably more like a sign wave shape.

    So I am thinking that I could accomplish this by using a frequency divider
    to shift the GHz frequency to a range (MHz) that my oscope could handle.

    Are there any big reasons why this would not work?

    --TIA, jw
  2. Apart from the frequency divider changing the shape and magnitude of
    the signal you want to measure the absolute value of - no, there is no
    reason why it won't work. :->

    Dave :)
  3. Kubiack

    Kubiack Guest

    Frequency divider are only useful for a frequency counter, where you
    don't care the shape of the signal...
    I think you have to buy a new scope...


    jw a écrit :
  4. Bob Masta

    Bob Masta Guest

    As others have noted, frequency dividers are typically
    digital devices that don't preserve amplitude.
    But if you just want to monitor the level of the signal
    (not it's wave shape) you can rectify and low-pass filter it and
    feed the DC to your scope. No, I don't have any handy
    GHz rectifier circuits handy... anyone else?

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  5. Chris

    Chris Guest

    The OP would have to provide quite a bit more information to get a
    recommendation for a homebrew circuit, like frequency range of
    interest, amplitude range, and impedance. Also, how would he check the
    results from any homebrew circuit, especially if
    amplification/buffering was required?

    It might be best for him just to do the job right and scrounge an RF
    voltmeter to make the measurement. They're commonly available
    used/reconditioned, and not very expensive. Some require special
    probes, so the OP should do his homework before buying.

  6. Don Bowey

    Don Bowey Guest

    Others have told you why that won't work. Here is one that will.

    You need to build an RF mixer to get the spectrum of interest to a frequency
    below 100 MHz.

    There are readily available VCOs and Balanced Mixers built for 1 GHz. Also,
    you should put a (100 MHz.) low-pass filter at the output of the mixer to
    eliminate the unwanted mixer product and to reduce the VCO Carrier leakage
    amplitude. With only a little care, the signal will be an excellent
    representation of it's form at 1 GHZ.

  7. jw

    jw Guest

    Thanks, this is great! --jw
  8. jw

    jw Guest

    I'll try a few things and get back if I run into trouble. thx, jw
  9. Jasen Betts

    Jasen Betts Guest

    yes, frequency dividers typically convert the output to a fixed voltage, not
    proportional to the input.

    A better move may be to use a downconverter (but that's about the limit of my
    knowledge of things RF)

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