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

[billriches]

Reminds me of the 1950's living in Wildwood, NJ.  We had a TV antenna on the roof to pick up stations from Philadelphia - 80 miles away.  When ever an airplane flew over you would see flutter and distorted sound!

73,

Bill, WA2DVU
Cape May

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of David
Sent: Tuesday, May 24, 2016 10:26 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

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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