[time-nuts] How can I measure time-delay of a cable with HP 5370B time-interval counter?

Dan Kemppainen dan at irtelemetrics.com
Tue Oct 30 10:49:01 EDT 2018



On 10/30/2018 9:55 AM, time-nuts-request at lists.febo.com wrote:
>>
> My MDO3024 (a modern scope) can measure delay and phase between two inputs,
> using the measured zero crossings, including statistics of the measurement.
> If you can obtain a similar scope, you could use two identical 1 Meg probes
> and a separate termination.
> 
> Regards,
> 
> Mark


Hi,

The problem with this is typically the sample rate of the scopes fall 
when looking at the lower frequencies, and you loose time resolution. 
With an MDOxxxx series scope setting the record length to 10M would help 
to keep the sample rate high. Then post processing the data external to 
the scope to best fit a sine may result in something you could use to 
calculate a good zero crossing.

I just tried a 10M length on the MDO3104, and that limits the sample 
rate to 2.5GS/s, about 400pS per sample with a few cycles of the sine 
available to look at. So it may be possible.

Also, Many scopes allow channels to be deskewed relative to each other. 
This would probably be something one would want to do before attempting 
a test like this. The MDO3104 allows deskew to a few pS, not sure about 
the MDO3024. If I get time I'll check the MDO3024 later.

Using a longer cable may help get this into a range where the 
measurement may be able to made with a good modern scope and a little 
post processing.

Dan



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