NOISE jamming...

[Dave Emery]

Steve Schear wrote :
> 
> A single jammer is an easy target but multiple coordinated jammers are a
> different story.  My group did some work at TRW on this.  Suffice it to say
> that just a few well coordinted jammers can make DFing even with satellite
> systems very, very, hard.

	There is quite a bit of emitter location technology around,
including much designed to work from airborne platforms that would
likely be deployed as soon as possible.   Seen from the air coordinated
jammers would  likely be widely separted spacially even if they weren't
as seen from the DSN antenna.  And an airborne platform can get very
much closer to one emitter (where its signal predominates) than others
making separating its energy from the rest much easier.

	But yes, a very sophisticated jamming effort sync'd up with GPS
timing and using multiple sites would be something that undoubtably
would knock out a station for a while as countermeasures to such an
attack are not part of operational plans for civilian science research
ground sites.   But many of those sites have several dishes of various
sizes with feeds at the downlink frequency and a dish with 50 or 60 db
of gain and tenth of a degree beamwidth would do fairly well at
isolating a single jammer azimuth and elevation by searching for and
pointing right at it. Perhaps it even would be possible to use two
dishes separted by enough distance to trianglulate.

> 
> >
> >	But most of the time Mars is visible from more than one DSN
> >earth station and given the high priority of the mission the most
> >likely thing would just be to switch stations to one a third of
> >the way around the globe or more.   Would obviously be a nuisance
> >and get some people very mad, but since the ground stations fail
> >from natural causes from time to time such a handover would be
> >fairly routine.
> 
> Which means you'd need to jam all the stations as they came into view.
> Certainly not the work of a lone hacker.

	Hell if you are dead set at disrupting more or less pure
science (mixed with a bit of budget sales pitch) why not rent a
Rider truck loaded with ANFO ? or a HERF device ?  or simply
start shooting at the antenna with a heavy gauge machine gun ?

	Or to be subtler and more stealthy, cut the fiber optic telco
cables connecting the site with the NASA network using nothing more than
a ordinary shovel and a bolt cutter in some out of the way spot.  Many
cable routes are well marked... and you could dress up as the gas
company or water and sewer department and nobody would think twice about
seeing you dig a hole by the side of the road.

> 
> Yep, I just thought they might employ FH to avoid the odd noise blips from
> terrestrial sources (even with reservation of the bands), although SS
> usually   increases front-end bandwidth and lowers sensitivity,
> selectivity, etc.  With link margins already low it probably doen't pay.
> 
	Hopping no,  But they have sometimes used direct sequence spreading
because it supplies a very accurate high resolution ranging yardstick
(as in the case of GPS which works exactly that way).

> >> >
> >	And would be spotted almost instantly on spectrum analyzers and
> >other monitors.
> 
> They'd certainly see the signal, but as I said above a coordinated attack
> from several transmitters can be exceedingly difficult to find, even by
> national technical means.

	Again, there are lots of flying (not orbiting) platforms with
various antennas and DF receivers that can do this sort of thing.
And they can fly any pattern that might be useful and look for interesting
visual, passive IR, and side looking radar observable objects on the ground.
Obtaining a rough (degree or so) direction on the jammers would be 
fairly easy using standard EMI horn and dish antennas or the automated
equivalent on military ELINT vehicles unless the jammers were using
very many sites closely spaced together and phase and frequency 
coherent signals from all the sites.   And certainly sweeping the horizon
with a big dish would likely yield significant location information
simply becuase of the very narrow beam width of the dish's main lobe.

	


							Dave Emery
							die at die.com
							Weston, Mass.