[time-nuts] GPS Jamming?

Dave Baxter dave at uk-ar.co.uk
Mon Nov 16 13:59:45 UTC 2009


Hi.

The "Monterey Bay" jammer, was indeed a UHF TV active antenna.  But, it
was hooting at about 1500MHz, that's what corrupted the GPS signals in
that area.   It's not unusual, there are many such documented cases from
all round the globe of similar instances, and it's not just GPS systems
getting hit either.   A recent case in the UK, a digital TV set top box,
was taking out the VHF comm's to a nearby local airport!  Lucky there
was an alternative channel to use, but it was found and "removed from
service".

As to "resistance to signals at the input"   That's probably for one
clean and stable carrier, like a local harmonic from a broadcast FM
receiver's own local oscillator.  I kid you not!  It happens, and is
again well documented in several cases, mostly in the US with one
particular make of SUV, suffering more than most, the symptoms being
that the built in sat-nav gave up, if you had the FM radio tuned to one
particular station!

It is all to trivial to successfully jam a spread spectrum signal..  You
just blot it out with another wide band signal, such as rapid sweeping,
or broadband noise.   Some systems are also all to vulnerable to pulse
type interference too (Terrestrial DTV for one!  OK, so not "true"
spread spectrum, but......)

The UK military often notify "other users" of "GPS Jamming Exercises" in
various places at odd times, all around the UK.   I don't know the
purpose of such "exercises" other than to perhaps prevent squaddies out
on a navigation training jaunt, not to cheat with personal GPS devices?
But I do know that the result varies from total loss of signals as the
receiver sees things, to a fix of sorts, but way off from where it
should be.

No doubt also screwing with any pps timing if that was in use.   (to
keep tenuously on topic?)

Unintentional emissions from electronic systems are one of the worst
things to find and fix.

Regards.

Dave B.



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