[time-nuts] [OT] repeater jammer

[Dave Baxter]

Repeater jammer?  Hmm....

A single semi resonant antenna, with a small signal diode at it's feed
(doesn't even need to be a VHF type!)  Then feed it from a 600kHz
oscillator (or whatever the repeater offset frequency is).  Running off
a suitable battery, build it small, throw it in a tree near the
repeater, wait for the mayhem to begin.   Better still, make half a
dozen of them and scatter them around near the repeater site, within
half a k should do.

They don't create a big signal on the input, just enough to keep the box
busy and 'P' off people, heterodynes all over the place...   Difficult
to DF too, as most DF kit will be swamped by the repeaters normal output
level.  Turn the box off, and the QRM goes away, so you cant even DF the
blasted things in the quiet.

If you felt 'really' malicious, you could put a simple random timer in
there too.  Total chaos!

That's what some bar stewards have done here in the UK in the past.
Then there are the sophisticated ones, with two FET's in them!   They
can be placed some miles away, for added inconvenience.

There has even been at least one with an "added ingredient" that needed
army types to sort out!  It was a dud thankfully by the time it was
found (by a bloke walking his dog!)

So, you can see that there is nothing new about any of this weird stuff.


The cheapest GPS jammer, is one of the common (but now ilegal, in the UK
anyway) re-radiating "GPS extenders", so you can run a handheld GPS RX
(with no external antenna facility) in a car with a heated or other
metalic coating on the 'screen.  If they see their own output, you can
nuke all civilian GPS activity for over a 1/4 mile radius!

Dave B.




> A *much* more effective and cheap strategy is a repeater jammer..
> Receive
> the signal and retransmit it: two antennas and an amplifier. The
> victim sees
> the delayed retransmitted signal at a higher level than the direct
> one. It's
> sort of like creating fake multipath interference. No need for PN
> generators, oscillators, etc.
>
> Granted, a smart receiver that *understands* the relationship
> between SV to
> user geometry and doppler can beat it (because the carrier phase and
> PN
> phase of the repeated signal won't be consistent with the geometry),
> but the
> run of the mill PN tracking loop probably won't.