On 10/2/12 7:33 PM, [email protected] wrote:
In considering the effect of a simple jammer on a GPS receiver, a simple
link analysis
is insufficient.
What must also be considered is the anti-jam capability of the receiver
which due to spread spectrum processing gain will reject any simple
jamming signal even though is it 10's of dB stronger than the desired
signal.
not most simple GPS receivers which have very little AJ capability. They
have a single bit quantizer (or maybe a 1.5 or 2 bit) after the LNA. If
the LNA doesn't saturate, then the quantizer is captured by the strong
CW carrier.
This is a classic problem with DSSS receivers and led to a lot of
research in the 80s on things like "adaptive excisers" to remove CW
carriers.
If you built a linear receiver with a lot of dynamic range, then, yes,
the process gain will suppress the CW tone, but you still have to
acquire the code, and as Dixon says (paraphrasing) "acquisition is the
secret sauce in spread spectrum systems". Back when I was doing this
kind of thing seriously (mid to late 80s), acquisition, particularly
robust techniques, were literally SECRET (in the DoD sense).
There have been a nice series of articles in GPS World over the past few
months about the variety of inexpensive GPS jammers out there. (and the
problems they cause).
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
