[FedCom] New antennas on the Secret Service suburban

[Dave Emery]

On Sun, Aug 08, 2004 at 10:09:36PM -0700, gary wrote:
> Unless they can localize the jamming, I just don't see how it could be 
> done without a notam. Airports have GPS approach patterns these days.

	I'm inclined to agree, it completely surprised me that there
would any chance of deliberately jamming such a vital service, used not
just for aircraft navigation but lots other uses including AVL systems
for tracking emergency vehicles and cell site time and frequency control
and many other critical uses.

	And there well may have been other explanations - what I
experianced is just an unexplained behavior of a device in my lab, a
behavior I have only noticed earlier when the antenna  connector came
loose (that wasn't the problem this time though).

	I did not attempt to use other instrumentation (such as a
spectrum analyzer) to try to diagnose the cause of the anomaly, I was
too busy following the  convention on TV and listening to convention
related radio traffic.   It was just something I noticed in passing
and fiddled with for a few minutes to see if the thing had gone belly
up for some reason.

	IF the problem was caused by RFI I'd actually be more 
inclined to guess that it might be strong signals (presumably in
L band somewhere) on OTHER than GPS 1575.42 mhz frequency that were
causing problems for my receiver (overload) than actually something
jamming GPS (especially for the whole Boston area).

	Civilian GPS receivers don't have all that tight rf preselection
so a strong signal nearby might have made the thing fail...  and that
incidently, might also explain GPS failure during POTUS visits
as well.

	And I frankly cannot entirely rule out interference from some
radio or another I had running at the time - I have observed that
certain scanners (RS 2006s amoung others) radiate enough local oscillator
signal in L band that if you tune them to the right frequency they
will jam nearby GPS receivers.   The antenna for my GPS standard is
some distance away on the rooftop above my lab/shack but it is possible
there could have been a problem.



-- 
   Dave Emery N1PRE,  die at dieconsulting.com  DIE Consulting, Weston, Mass 02493