[time-nuts] GPS fadeout

Björn Gabrielsson bg at lysator.liu.se
Wed Aug 22 01:23:03 EDT 2007

On Wed, August 22, 2007 1:26, Hal Murray said:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+bg=lysator.liu.se at febo.com RETRY
> I'm trying to check/debug some new software so I'm paying attention to the
> output of a Garmin GPS 18 USB.
> It's inside my house, not a great location.  Mostly, it works.  But every
> now
> and then it fades out for a few minutes.

Start logging a quality measure for each satellit vs time vs
elevation&azimuth. There is always a message giving some kind of SNR.
After a few days you should have a good "map" of what sky positions get
through to your receiver and what the normal "quality" is at each

Also note that the 20dB crosscorrelation resistance of the CA code is not
all that good. If you get a single SV directly through a window it might
be more than 20dB stronger than others going through the house and
effectivly jam the weaker signals.



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