[time-nuts] comparing two clocks

Bob Stewart bob at evoria.net
Sat Feb 22 14:16:24 EST 2014


Hi Jimmy,

Someone touched on the idea of using a scope.  Go to the Agilent site and download a copy of the 10811 manual, 10811-90002.pdf.  Section 3 describes how to adjust the 10811 and gives info on how to time the phase drift to calculate the frequency error.  You can pull the time base out of the back of the counter and use it as one of the inputs to the scope for this measurement.  


For that matter, you should be able to send the time base back into the counter for a Time Interval measurement against your other oscillator.  However, that won't give you much value unless you have a GPIB adapter and can capture the time interval value over some period and make pretty phase plots and do ADEV plots.  You can get useful values a lot quicker using the method in the 10811 manual.  


Regardless of which method you use, you will quickly wonder which clock is being measured.  Once you ask that question, a GPSDO is in your future.  Been There, Done That.  Still doing it.


Bob - AE6RV




>________________________________
> From: Jimmy Burrell <jimmydburr at gmail.com>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Saturday, February 22, 2014 7:17 AM
>Subject: [time-nuts] comparing two clocks
> 
>
>I need some help with a 'noob' question regarding some practical examples in some of the NIST literature. When attempting to compare two clocks, I'm a bit confused on the subject of exactly how to use my counter to compare a delayed clock relative to another. Or perhaps I should just say 'comparing two clocks'. Let's take some concrete examples. 
>
>Let's say I want to characterize my Morion MV89 ocxo using my HP5335a. Obviously, I can tune the MV89's 10MHz by +/- 1Hz and feed it to the counter's input 'A'. Obviously, I can feed in a second, external reference clock at 10MHz into input 'B'.  Suppose, however, I didn't have an external reference clock. Can I compare against the counter's internal time base by hooking a line from the rear jack time base output to channel 'B' input? Or am I making it too complicated? Do I simply plug into input 'A' and go?
>
>In a somewhat related question, in this article (http://www.wriley.com/Examples%20of%201%20PPS%20Clock%20Measuring%20Systems.pdf) where two clocks, both divided to 1PPS, were compared, W.Riley makes the following statement, "The two 1 PPS outputs were connected to a Racal Dana 1992 time internal counter having 1 nanosecond resolution, and the start and stop signals were separated sufficiently in time for the counter to function properly".  I wonder what exactly is meant by "separated sufficiently in time for the counter to function properly" and how one would go about doing this? For example, is inverting one of the signals sufficient separation? If not, how is this typically done? Delay line?
>
>Thank you,
>
>Jim...
>N5SPE
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