[time-nuts] Delay through GPS antenna splitter/amplifier -- an answer, and a question
Rob Kimberley
rk at timing-consultants.com
Mon Mar 12 17:38:28 UTC 2007
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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