GPS "Testing"

[Chip Fetrow]

Mike:

I doubt that jamming or testing was your issue today.

Today's GPSs assume they are turned on where they were turned off.
They check the almanac and try to lock based on that location, and the
time.  If they don't find the satellites where and when they think
they will be there, the expand the search.

Also, the geometry of the birds can make a difference, especially if
you are inside, or don't have a full view of the sky.

My TomTom finds the birds in SECONDS if I turned it off where I turn
it on.  If I fly cross country, it can take many minutes.  My old
Garmin Street Pilot III used to fail if taken cross country.  It would
ask if it should keep trying, go into simulation mode or if I wanted
to give it a location.  If I gave it a location, it would lock up
sooner, but even if I didn't, it would eventually find the
satellites.  I still use the thing, but for situational awareness,
along with the TomTom.

--chip

On Jan 21, 2011, at 6:59 PM, tacos-request at rf.org wrote:

> Message: 4
> Date: Fri, 21 Jan 2011 11:53:31 -0800 (PST)
> From: Michael Chisena <ka2zev at yahoo.com>
> To: tacos AMRAD <tacos at amrad.org>
> Subject: GPS twitch
>
> Guys,
> Just what would the symptom be with this disturbance in the GPS force?
>
> On the bench today my little GPS sensor took a long time to lock up.
> Usually they acquire and send good data in about 30 seconds from a
> cold turn on.
>
> Today it took over 4 min.
>
> Thanks in advance.
> Mike in Herndon
> KA2ZEV