[time-nuts] GPS fadeout

[Bruce Griffiths]

Tim Shoppa wrote:

  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.

Tim.


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Tim



Even with a relatively jam resistant timing antenna, low RFI and little
air traffic, if the antenna location is suboptimal dropouts of this
nature can occur.

Trees and structures within the building can create narrow regions of
the sky where the satellite signal strength is severely degraded.



Bruce