[time-nuts] Question about an HP5370B TIC

Bob Smither smither at c-c-i.com
Sat Oct 1 22:51:29 UTC 2011

John Miles wrote:
>> As long at there is always a positive or always a negative time
>> difference between the two 1 pps signals the result makes perfect sense.
>>   There appears to be about a 2 to 3 usec jitter in the 1pps from the
>> GPS (this is expected given the design of the receiver).
>> If I put the 5370B in the +/-TI mode I expected to see both + and -
>> small time differences when the two signals are closely aligned - and
>> mainly I do.  Typically the difference is + or - a usec or less.
>> Occasionally however the 5370B displays very near to a +1 or -1 second
>> (999.999 xxx ms or -1.000 000 xxx s for example) reading.  Needless to
>> say this plays havoc with trying to measure a mean value of the
>> alignment.  The 5370B is clearly measuring the "outside" between the
>> pulse pair when I want it measure the "inside" (or short time interval)
>> between the pulse pair.
>> Is this normal behavior?  Is there a setup that I am missing to make it
>> do what I want?
>>From what I've seen it's best to stick with +TI mode for measurements like
> this.  You don't want the counter making decisions about which half of the
> interval is "short" and which half is "long" -- it just doesn't add any
> value to the measurement.  

Thanks John.  I moved the OCXO edge about 100 usec after the GPS 1PPS 
and now I can use the +T1 mode.  It just seemed more "natural" to try to 
line up the edges.

 From your response I am going to assume that the behavior I observed is 
in fact normal and my 5370B is OK?

Best regards,

Bob Smither, PhD                                        Bob at Smither.net

          A flag you can burn ... is the only kind worth dying for.

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