purple_stars wrote:
Da Kine wrote:
[snip]

In your reading, pick up a red/orange colored paperback called
"Emergency Navigation". Its available all over and you should be
able to find it at http://www.amazon.com for cheap. You won't find
much of the good stuff in most books.


good stuff, i will check into it ...


As for something else making GPS not work, there are a few things I
have come across and here they are.


i spent a little while reading about this since my last post and found
some interesting things i didn't know, i'll post some of them here
since you are interested too! from some of the things i read it looks
like GPS does/has failed before, i didn't know that before now.
there's a quote in one of these documents that i found interest, the
document says the quote is from "Interagency GPS Executive Board. GPS
policy, applications, modernization, international cooperation.
February 01". here's what it says ...

"GPS provides many benefits to civilian users. It is vulnerable,
however, to interference and other disruptions that can have harmful
consequences. GPS users must ensure that adequate independent backup
systems or procedures can be used when needed."

then later in that same document it is talking about situations where
GPS doesn't work, and apparently it's pretty easy to make it not work!
you can build GPS jammers using plans on the net to jam GPS signals,
and there are even jammers sold for doing the same thing. one paper i
read said that these jammers are sold to militaries that want to be
able to selectively jam areas for security reasons, and to defend
themselves from attack, and that some of these jammers are huge like
radio stations.

this one paper i read had these real world situations where GPS had
failed ...

"Jamming in Mesa, AZ
13 - 18 Dec 01, GPS jammer caused GPS failures within 180nm of Mesa,
AZ
Boeing was preparing for upcoming test
Accidentally left Jammer on L1 frequency radiating at .8mW
Jammer operated continuously for 4.5 days
Impact to ATC operations
A/C lost GPS 45nm from PHX, performed 35° turn toward traffic
NOTAM was not issued until 2nd day
Numerous pilots reported loss of GPS NavAid
Reports of hand-held GPS receivers not working"

"Jamming in Moss Landing Harbor, CA
15 Apr 01 - 22 May 01, VHF/UHF television antenna with pre-amplifier
caused GPS failures to all of Moss Landing Harbor
Boat owner purchased TV antenna, which was equipped with pre-amp
From interior location Amp's emitter jammed all of Moss Harbor and
1km out to sea
No GPS in entire area = 37 days
Impact to Moss Harbor
Research vessels relied heavily on timing from GPS
Extreme difficulty going through harbor in foggy conditions
Notification to all vessels in area that GPS was down
Switched back to radar control for harbor entrances"

The jamming of GPS is possible and used. The challenge is long range
jamming or continuous jamming. It takes a great deal of power to jam a
GPS that is any distance away. It also needs to run continuously to
really screw you up. Once the jamming stops, or you get too far away,
it just locks back on. The jamming will likely be obvious. You just
won't get a signal. The better way of doing it is not jamming but
deceiving the GPS so it looks like it is working but leads you (or a
missile) away from the intended destination or target. This would be
fairly obvious on a yacht at sea.

In other words, don't worry about it. The 90% of the time you are on
your boat sitting at anchor it won't matter. The rest of the time
nobody cares to jam you.

Don't forget that tinfoil in your ball cap.