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fast frequency counter question

Discussion in 'Electronic Equipment' started by Don, Jul 28, 2004.

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  1. Don

    Don Guest

    I am having a problem find a frequency counter/time interval analyzer
    that is capable of the following

    Reasonable accuracy at
    * Measuring 15MHz signal
    * take parts per billion (in Hz) at 10 Hz sampling rate

    Is anyone aware of such an instrument. On the counters I've checked
    out so far you are lucky to get ppb resolution in 1 or 2 seconds.
    Someone else mentioned the possibility of mixing the signal with a
    similar rate in order to get side bands and measure those. That is a
    little outside my normal "just take the frequency" realm. How
    difficult would that be if there is no equipment available that will
    do the 10Hz sampling at ppb ?

    Thanks.
     
  2. mike

    mike Guest

    Sometimes your first thoughts at how to do something are not optimum.
    Try recasting the problem so you don't have such a hard measurement
    problem to solve. Any time your exponent is "10", you've got a
    measurement problem.

    Explain what you're trying to accomplish and you might get some useful
    ideas.
    mike

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  3. Bill Janssen

    Bill Janssen Guest

    The way I would TRY to do that is to measure the phase difference of
    the reference and test signal
    every 1/10 of a second. The accuracy of the phase test will determine
    the accuracy of the
    measurement.

    I think you will find that the test is not easy to do at 1/10 second per
    sample rate. Try 10 second
    per sample and maybe it is doable.

    Bill K7NOM
     
  4. Don

    Don Guest

    Actually I seem to have solved my own question. An agilent 53181 can
    do this measurement okay over the gpib bus, if you shut down every
    single function other than gpib communication and frequency
    measurement functions (blank the LED readout, shut off stat/math
    functions, etc). The error of the measurements is the same as that of
    the manual readings i've taken with longer acquisition times (5
    seconds as opposed to the 100 milliseconds I originally intended on).
    Measuring a 15 MHz (pure tone, I should have specified) doesn't seem
    to be a problem out to 10 digits. Thanks for the responses, I don't
    know what else I could have specified other than it is a 15 MHz signal
    and I wanted parts per billion resolution with a 10Hz sample rate.

    Thanks.
     
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