[time-nuts] Frequency Stability of Trimble Mini-T
Tom Van Baak
tvb at LeapSecond.com
Tue Oct 14 19:38:19 UTC 2008
I keep hoping to find a Mini-T on eBay but no luck yet and so I
don't have plots on my web site for that unit. Does anyone have
Question on the spec and on your plot, though. What is the gate
time of the frequency measurements? If you average for an hour
or a day many of those peaks would melt.
Also most look like phase jumps not frequency jumps. When you
see frequency jump up and then down by the same amount as a
pair it's usually the result of a single phase jump.
Did you log sats-in-view, or DOP, or temp during your run to see
if the jumps correlated to that?
Finally, "frequency drift" is not at all the same thing as "frequency
excursions", so what did they really mean?
> The attached URL is a 11 day plot of a 30.5 GHz carrier taken every minute
> by an Agilent 53152A microwave counter. The Mini-T has an ovenized
> oscillator. It appears that the GPS attempts to over correct the oscillator,
> hence the large frequency excursions. The real large excursions, around the
> 96 hour range, were due to a loose connector. The requirements are such that
> over a 90 day period the total frequency drift shall be no more than 1 KHz.
> Someone in their ultimate wisdom, decided that since they do not have the
> time to take measurements for 90 days, they will take it for 24 hours and
> not allow any frequency excursions over 11 Hz at 30.5 GHz. Obviously, this
> plot does not pass their requirement. When the oscillator is allowed to free
> run, the frequency jumps are not there. Has any one else made any
> measurements on the Trimble Mini-T. Any observations or suggestions are
> appreciated. Regards - Mike
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
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