fast frequency counter question

D

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.
 
Don wrote:
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.
Click to expand...
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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Don wrote:

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.


The way I would TRY to do that is to measure the phase difference of
Click to expand...
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
 
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.

fenriswolfnews@hotmail.com (Don) wrote in message news:<fcfccb29.0407280703.7ba48475@posting.google.com>...
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.
Click to expand...
 
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