On Sun, May 21, 2000 at 01:07:11PM -0700, Phil Karn wrote:
> >Sounds like some interested parties should take some GPS gear and some
> >radio receiving and test gear to one of the spots where the millatree
> >is warning airmen that "for the next two weeks, GPS doesn't work
> >here", and see just what sort of jamming they are using...
>
> A good idea, but I note that most of these sites are in the middle of
> large western military reservations out in the middle of nowhere. You
> might be able to see something from a small plane (keeping out of
> restricted airspace, of course) but then you need some other way of
> knowing where you are so you can compare results.
The only tests around the east coast have been offshore in the
SE, and given the increasing dependance on GPS by business and commerce
and telecommunications timing and frequency control, holding such things
near the major population corridors is less and less an option. So for
me, at least, such an interesting investigation would mean equiping a
mobile laboratory, driving across the continent, and hoping I could get
close enough to the jammer somewhere out in the high desert in Utah or
Nevada to see the jamming signal. I suppose if I didn't get really airsick
flying in small planes that might be the way to handle this, but I'm
not enthusiastic about cleaning barf off the spectrum analyzer.
What one really might want to do if doing this right is use one
of the Agilent (nee hp) boxes that digitize a whole chunk of spectrum
using about a 20 bit A/D and dump it to a fast disk array. I think
there is a version that could be persuaded to handle the entire spectrum
around the open L band C/A signal with the required timing and frequency
accuracy and bandwidth. Of course spacial information about the jammer(s)
would also be interesting and this would probably require synchronized
capture of signal from multiple antennas with known positions relative
to each other allowing DFing of the signal components by DTOA methods.
In theory, of course, one could equip an aircraft or vehicle with
this gear and make a run and then grovel through the resultant capture
at one's leisure over weeks or months, at least if one was lucky enough
to catch the jammer in operation and from a good vantage point.
>
> Phil
--
Dave Emery N1PRE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass.
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
