[aprssig] GPS Jamming On The Rise

Rich Garcia k4gpsc at gmail.com
Sun Jun 29 19:51:50 CDT 2008


It has been many years but the 3rd harmonic of analog CH 67 I belive is
right on top of the GPS signal. One of my cell sites was co-located with a
TV station and we often had very serious problems locking up our XO and RB
that got a reference off of the GPS receiver (a Motorola Oncore BTW that was
built into the XO).

If the GPS ever died we would never be able to swap of the XO without
powering down the TV station, talk about a pain. In my 8 years there we had
to power down the transmitters for about 2-3 hours on 3 occasions. Yes we
would get lock quickly but the database was slow to update, if all birds
were not seen and "memorized" off the bat when the TV station powered up we
would lose the lock. After several hours we were able to power the TV
transmitters up and from 6-7 birds it would drop to 3.

Eventually by mounting the GPS antenna at a 45 degree angle away from the
tower and on the ground BEHIND A 16ft dish that blocked the view from the
broadcast antenna we were able to resolve MOST of the trouble.

-----Original Message-----
From: Greg D. [mailto:ko6th_greg at hotmail.com]
Sent: Sunday, June 29, 2008 8:09 PM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] GPS Jamming On The Rise

1.something.  What is it, 1.6?  More than the 1.3 that I can get to....

Greg  KO6TH

> Date: Sun, 29 Jun 2008 15:34:18 -0700
> From: n6lrv at cox.net
> To: aprssig at lists.tapr.org
> Subject: Re: [aprssig] GPS Jamming On The Rise
> GPS doesn't operate at 1.7Ghz.
> "Greg D." wrote:
>> Interesting...  So, for us Hams to assist in this sort of DF'ing, all we
need is an ICOM R3 receiver?  Are there any other portable receivers capable
of covering the 1.7 ghz part of the spectrum?  My Kenwood TH-F6 tops out at
1.3 ghz, as does my old ICOM IC-R7000 receiver.  I figured we'd need to
create something custom...
>> This seems too easy...  Are there jamming sources that aren't as easily
detected by a hand-held scanner?
>> Greg  KO6TH
>> p.s.  I also experienced the Garmin reverse-jamming scenario.  The
solution was to wait (8+ years) for my GPS-III to wear out - the display is
getting multiple stripes of bad pixels across it- and replace it with an
eTrex Vista HCx.
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