[time-nuts] FTS4060 Continuing Saga
dforbes at dakotacom.net
Sun Mar 5 17:11:03 EST 2006
At 12:02 PM -0800 3/5/06, Brooke Clarke wrote:
>After Tom helped me a month ago to get the trigger level correct for
>50 Ohm loaded TTL (1.25 volts), I've been seeing no aging on the
>FTS4060 s/n 1013 and have been tweaking the C field and all was
>going well, but today (heavy rain) the jitter on each 500 second
>average has jumped up from about 9 ns to more like 300 ns which
>means you can not believe the readings. It's snowing on the nearby
>mountains and heavy rain here.
>Note that on prior days the daily spread in the Time Interval has
>been around 10 ns peak to peak.
>So does GPS suffer with heavy rain?
>I checked TAC32 and the receiver settings are correct.
Rain should have an effect on the timing of the signal, since the
propagation speed of radio waves through water is different from that
through air. It will also attenuate the signal, causing worse S/N
ratio which would cause the lower-elevation satellites to not be seen.
An interesting confirmation would be to look at the Lat.-Long.-Alt.
coordinates determined by your GPS receiver (assuming it's not a
timing-only model) to see how they vary through a rainstorm. I'd
expect altitude to change, and/or the fit to the ephemeris to be much
worse than usual.
--David Forbes, Tucson, AZ
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