[time-nuts] Delay through GPS antenna splitter/amplifier -- an answer, and a question

[Rob Kimberley]

UTC-GPS is based on UTC-USNO, and therefore there will be a small offset
between other establishments like NIST, NPL who contribute to the UTC. 

As you say, the offset will vary with time, so post-processing is the answer
in critical applications (which is the way UTC is determined anyway).

Rob K 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Ackermann N8UR
Sent: 12 March 2007 16:51
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier -- an
answer, and a question

In short, yes.  If you want true traceability to NIST, you need to take into
account UTC(GPS) versus UTC(NIST).

I don't think you would do this by adjusting the cable delay, because that
offset will change over time.  Instead, you post-process by getting the
offset for the time during which you made the measurement, and adding it to
your solution.

John
----

Jason Rabel wrote:
> Since we are on the subject... I came across this page the other day 
> and am curious about what other's thoughts are about it.
> 
> http://tf.nist.gov/service/gpstrace.htm
> 
> If I understand correctly looking at the graphs, they are saying the 
> time from GPS is currently off about 24-30ns from the NIST frequency 
> standard. So does that mean that a person wanting every last ns should 
> adjust their delay according to the data on that page (and of course 
> things like cable delay and other circuitry)?
> 
> Jason
> 
>> But we're time-nuts... we DO worry about those things. :-)
>>
>> While we were at it with the network analyzer, we did FDR (frequency 
>> domain reflectometry) to measure the cable delay to the antenna, and 
>> I spent yesterday making up six matched cables to go from the 
>> splitter to the receivers -- they all test within about 1 nanosecond of
each other.
>>
>> Obsessive compulsive?  Me?
>>
>> John
> 
> 
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> 


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