AW: AW: [time-nuts] Strange effect with C-Field change
John Ackermann N8UR
jra at febo.com
Thu Mar 24 16:58:38 EST 2005
Hubert v. Bonhorst wrote:
>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.
Hi Hubert --
That's a good hypothesis, but given how long this system (same receiver
and antenna) has been running without ever encountering something like
this makes me doubt it's a GPS anomaly, or at least a local one. A long
history has shown that this receiver/antenna very seldom loses lock, and
the only strong transmitters nearby are in my hamshack, and were shut
down while I was out of town.
Actually, right now I'm suspecting it might be a cabling problem (a
possibly intermittent cable on the 1pps to the TIC that moved when the
door to the 5061A control panel was opened), though it's surprising that
something like that would result in more than a very transient phase
shift -- I'd expect to see a transient in one data reading, not
something that happened over hours. I'll be doing some tests to see if
I can reproduce the jump when the cable is moved.
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