[time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

David davidwhess at gmail.com
Tue May 24 22:26:14 EDT 2016


On Tue, 24 May 2016 16:15:15 -0700, you wrote:

>
>kb8tq at n1k.org said:
>> The glitches are to narrow (short duration) and far to regular for the
>> ionosphere to be the issue.  
>
>Is multipath from a large airliner in a landing pattern likely to cause that 
>sort of problems?
>
>I'm 20+ miles off the end of SFO, but it's common to see large planes going 
>over and turning to line up for a landing.  On my one-of-these-days list is 
>to grab the airline location data and see if it correlates with GPS glitches.

Back when I did a lot of transmitter hunting, I listened to multipath
from airliners from 2 meters to 23 centimeters.  The 2 meter
directional antenna I ultimately designed was good enough to not only
track airlines by their reflected RF, but it could see reflections and
shadows from nearby objects like street lights and trees which
ultimately limited outside performance testing.

As you can calculate from the geometry, the flutter started out fast
and decreased in frequency until there was a slow null/peak and then
it reversed.  If the same happened with GPS, then maybe the receiver
could briefly lock onto the reflection from the plane producing a
different solution for a short time.


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