AW: AW: [time-nuts] Strange effect with C-Field change
Hubert v. Bonhorst
hvonbonhorst at t-online.de
Thu Mar 24 16:40:01 EST 2005
I saw similar outliers running especially Motorola GPS receivers in the
vicinity to mobile telephones. Shielding is not sufficient. What I see in
your data plot is a drifting oscillator until the receiver tries to find a
new satellite configuration. (sudden jump upwards). After some time the
receiver just changes phase. At the moment of relock (sudden jump downwards)
the mobile or whatever source of distortion to the receiver is removed.
Might be the receiving antenna was covered, by whatever material you can
imagine. The 5061A did not loose phase during this period of time. Now its
time to verify, why the receiver did not work.
Von: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] Im
Auftrag von John Ackermann N8UR
Gesendet: Donnerstag, 24. März 2005 21:29
An: Discussion of precise time and frequency measurement
Betreff: Re: AW: [time-nuts] Strange effect with C-Field change
Hubert v. Bonhorst wrote:
>If you disregard this excursion, what happened after the change. Did
>frequency change as expected? Would there have been continuity of data?
>Which TIC do you use? Which GPS receiver do you use? How many satellites
>you track? What is the minimum elevation for satellites used?
>I know a lot of stupid questions, but ....
Hi Hubert --
Yes, after this "blip" that lasted several hours the phase abruptly
returned to just where it was. After things returned to normal, the
frequency offset appears to have changed as expected (though I still
need to gather data for another couple of days to precisely determine
the offset). The TIC/GPS setup has been running continuously for a
couple of weeks (and I've been doing similar measurements with basically
this same set-up, though sometimes using a different TIC, for a couple
of years). I've never seen a shift of this magnitude before.
It might have been a GPS anomaly, but the coincidence of the event
happening just as the C field was changed is hard to ignore. Following
Tom's suggestion, the next step is to (very) carefully see if Jody might
have done something else while making the change.
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