[time-nuts] GPS jamming susceptibility

[John Green]

Given that this is an extremely sensitive topic and completely illegal
also, let me just state at the outset that I have no interest in
jamming anyone's GPS. A while back, I was looking at one of those
Chinese discount electronics websites, I'm sure we all have, and
noticed a GPS jammer for sale. I had been wanting to do some jamming
susceptibility testing for quite some time but had never got around to
building a generator to test with. The thing was cheap so I ordered
it. After it arrived, I opened it up, first thing, to see how it was
made. It has a dual 555 oscillator, a couple of analog switches, a 1.9
GHz VCO, a single amplifier. It doesn't look capable of putting out
more than 50 milliwatts or so into a 2 inch antenna. I was somewhat
dubious that it would do anything, so I took it to the bench where the
Z3801 lives and turned it on. Within 2 seconds, the holdover LED lit.
I immediately turned it off and within a few more seconds, the
holdover LED was back off. The GPS antenna is perhaps 35 feet away
with a cinder block wall, a brick wall, and a metal roof in between. I
also put a 15 Db attenuator between it and the antenna with almost the
same result. I am going to do more testing with it wired into the GPS
downfeed an an adjustable attenuator in line just to see how much
signal it takes. That way, there will be little danger of messing with
anyone's reception. It is just a simple sweeper so it must do its job
by brute force. I am amazed that it took so little to shut my Z3801
down. Has anyone here had any actual experience testing GPS receivers
for susceptibility?