[PUP] AIS pitfalls

[Dave Cooper]

<Ron wrote: The USCG announced that the Navy in our area of North Carolina
would be conducting tests that would disrupt both GPS and AIS. The latter
would have to be a discrete frequency interference to avoid disrupting
normal VHF safety communications.>

Thanks Ron, this further confirms the point of pitfalls.
However the AIS transponder will receive the false or modified GPS signal so
it will give bogus location, course and speed data.
The heading and other data is independent of the GPS so they would show
normally.

If the data is scrambled then they are using a VHF frequency transmitter and
the VHF transmission would be affected...I doubt that this is what they are
doing. If just the GPS data is affected then it's the satellite signal that
they're messing with. A more likely scenario.

This illustrates a bit more of what I've been trying to get across in my
poorly worded rants here. The blending of these technologies, some old some
new, into a yet newer package makes it hard for a lay person to understand
who's on first. It looks like it also makes it hard for an AIS knowledgeable
person to figure it out also.

If you jam or spoof the GPS signal the whole of AIS in the area of the false
signal is worthless along with all the other 7 GPS's we have doing whatever
they do. If you jam the VHF AIS frequency only you only affect the AIS and
nothing else. A doubtful exercise, IMHO.

I guess the tows in this area will even be more confusing with their
projected lines, symbols and location. Better get Penny and John down there
to direct traffic ;-)

As always YMMV....

Cheers

Dave & Nancy
Swan Song
Roughwater 58
Caribbean Cruise '07