fast frequency counter question

- D
- Don
  
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posted
19 years ago

Wed, Jul 28, 2004 3:03 PM

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.

- M
- mike
  
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posted
19 years ago

Wed, Jul 28, 2004 7:32 PM

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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- Bill Janssen
  
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posted
19 years ago

Wed, Jul 28, 2004 8:45 PM

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

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- Don
  
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posted
19 years ago

Thu, Jul 29, 2004 7:38 PM

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.