[FedCom] New antennas on the Secret Service suburban

[Tom Greenwood]

I find localized error to GPS as a function of the overall GPS network of
satellites to be highly unlikely.  It would be difficult at best to affect
the timing of three or more satellites  to induce an error to such a
localized area due to the size of the foot print of each satellite at any
given time.  However, inducing localized errors via direct transmission of
interference in a localized area is very much possible.  As the received
signal strength from each satellite is theoretically below the noise floor
of the receiver, the signal would not have to be very strong to cover such a
small area.  This very characteristic would also make it very difficult to
detect an intentioal jammer in the area.  Anybody ever notice any strange
vehicles or antennas during such occurences?  Has anybody ever verified the
PDOP and HDOP values as reported by the GPS receiver when in those areas?

Tom


-----Original Message-----
From: fedcom-bounces at mailman.qth.net
[mailto:fedcom-bounces at mailman.qth.net]On Behalf Of john wilson
Sent: Tuesday, August 10, 2004 12:23 PM
To: Discussion of Federal Government Communications
Subject: Re: [FedCom] New antennas on the Secret Service suburban


    I also have a Garmin V.  I live near a military installation with an
interstate connection highway relatively close to one side for a few miles.
For a certain distance  of approximately 1-2 miles I and a few other ham
radio
locals using GPS receivers/mapping programs have noticed a phenomenon.  The
GPS receivers  have no problem acquiring satellites but the  mapping program
display GPS tracking graphic executing on a laptop in the vehicle will be
noticeably off for that stretch of road.  This occurs when using Mapsource,
Street Atlas 2003 and Street Atlas 8.  I am not the only one locally
experiencing this occurrence and I doubt that all the mapping programs would
have the same problem.  This erroneous display occurs only in this one area
and there is no RFI source nearby.  At a particular location on the
interstate
the GPS tracking graphic returns to a dead on display of the road which is
the
typical occurrence.

  The local consensus is there is a built in GPS error for these selected
latitudes and longitudes locations.  I think it is possible for GPS software
to be programed for such situations.  We all know that there is a deliberate
in error for the GPS downlink signals.  It is conceivable and possible that
for selected latitudes and longitudes additional GPS built in errors could
be
programed.  Currently piloted aircraft have no problem compensating with the
built in error or with the add on interface that reduces the error.



bernieS wrote:

> curiously, my Garmin GPS-V failed to get a fix on *any* GPS satellites
> during a public outdoor POTUS speaking engagement (it was fine before
> and afterwards...)
>
> can anyone else verify this phenomenon?
>
> On Sun, 8 Aug 2004, MONIX wrote:
>
> > Take your service monitor or spectrum analyzer.
> >
> > >>This makes more sense, and jamming has worked recently to
> > >>protect Principals from command detonated threats until the
> > >>convoy has passed.<
> >
> > >That's a very interesting suggestion. The POTUS will be in my area next
> > >week, so we'll have to see if it shows up here.
> >
> >
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> >
>
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