[time-nuts] GPS fadeout

Tim Shoppa shoppa at trailing-edge.com
Tue Aug 21 19:36:37 EDT 2007

Hal Murray <hmurray at megapathdsl.net> wrote:
> 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.
> I'm only logging the data every minute or so, but I have counts of the 
> good/bad seconds.  On the glitch that just happened, it was going fine with 5 
> satellites.  Then it faded out to 0 satellites.  Two minutes later it had 5 
> satellites again.  The total even was under 4 minutes.
> Are glitches like that common?  Does anybody have a list of what causes them?
> The only thing I can think of is multipath off an airplane.  Big jets are not 
> uncommon overhead.  I'm ~30 miles south of SFO.

Local VHF/UHF transmitters such as public service
base stations or even mobile units can desense consumer GPS antennas easily.

RFI-resistant GPS antennas (commercial and/or military) are available.


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