Gary wrote:
[snip]
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.

i never said i was worried about it. i never said i thought anyone was
going to jam me. i never said i was going to high latitudes where i
thought geomagnetic storms would affect me. all i did was answer my
own question which was "can GPS fail ?". to my surprise, yeah, there
were some cases where it has failed. end of story.

GPS is a great tool, my primary navigation tool and i would assume the
primary navigation tool of anyone on a boat. i can't imagine any
reasonable situation where it would ever fail for me. but that doesn't
make understanding when it can fail some kind of crime, it doesn't make
me into some kind of anti-GPS zealot.

Don't forget that tinfoil in your ball cap.

i don't understand why you are being rude to me, i've not done anything
to you.

chuck wrote:
Take a look in your local library for a copy of the Radio Amateur's
Handbook. You'll find a discussion there on building small loop antennas
that can be pretty effective in RDF work.

Another option is to check Ebay from time to time for used RDF gear.
Heathkit made a lot of marine RDF units over the years and these are
usually priced reasonably.

thanks chuck, sounds good.

i tried this evening to tune my icom ic-706-mkiig to listen to an NDB
(non directional beacon) at the local airport, failure! i couldn't
figure out why it didn't work either, i was within about 6 miles of one
of the transmitters and that transmitter was listed as being 25 watts,
so i should have had no trouble picking it up even with the crappy whip
antenna i had. but i couldn't hear a thing out of it, just static.
turns out that my icom radio is pretty much deaf as a post below about
300khz, and these transmitters were down in the 200-250khz range. oh
well, i guess i'll just get one of those marine RDF units and be done
with it lol, they can certainly tune to an NDB and listen to it. i
guess hearing it on my icom radio wouldn't have been a big
accomplishment anyway even if it had worked ... except that i could use
the opportunity to listen to the slow speed morse code, i'm still
learning CW/morse and haven't been practicing!

Your 706 is probably OK. The problem is that the whip's impedance is a
really poor match to 50 ohms at those long wavelengths. The marine VLF
radios use either an active antenna that performs the impedance
transformation or a special ferrite matching coil.

Try using a long metal fence or something similar and see if that makes
a difference.

Chuck


purple_stars wrote:
chuck wrote:

Take a look in your local library for a copy of the Radio Amateur's
Handbook. You'll find a discussion there on building small loop antennas
that can be pretty effective in RDF work.

Another option is to check Ebay from time to time for used RDF gear.
Heathkit made a lot of marine RDF units over the years and these are
usually priced reasonably.


thanks chuck, sounds good.

i tried this evening to tune my icom ic-706-mkiig to listen to an NDB
(non directional beacon) at the local airport, failure! i couldn't
figure out why it didn't work either, i was within about 6 miles of one
of the transmitters and that transmitter was listed as being 25 watts,
so i should have had no trouble picking it up even with the crappy whip
antenna i had. but i couldn't hear a thing out of it, just static.
turns out that my icom radio is pretty much deaf as a post below about
300khz, and these transmitters were down in the 200-250khz range. oh
well, i guess i'll just get one of those marine RDF units and be done
with it lol, they can certainly tune to an NDB and listen to it. i
guess hearing it on my icom radio wouldn't have been a big
accomplishment anyway even if it had worked ... except that i could use
the opportunity to listen to the slow speed morse code, i'm still
learning CW/morse and haven't been practicing!

Wayne.B wrote:
On 5 Mar 2006 14:20:24 -0800, "purple_stars"
wrote:


waynes i'm guessing that you mean that the navy doesn't teach RDF, not
that they don't teach celestial. only reason i say that is because it
seems like the military would need backups like celestial because i
understood that the EMP from a nuclear weapons blast could take out
electronics such as GPS systems. is that wrong ?


Yes, it's wrong. They no longer teach celestial.


You keep saying that. However, celestial navigation is shown as part
of the navigation course at the Naval Academy, which is required for
many majors.

The report from a few years ago which created your myth was that
celestial was no longer required for *all* majors.

purple_stars wrote:
Gary wrote:
[snip]

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.


i never said i was worried about it. i never said i thought anyone was
going to jam me. i never said i was going to high latitudes where i
thought geomagnetic storms would affect me. all i did was answer my
own question which was "can GPS fail ?". to my surprise, yeah, there
were some cases where it has failed. end of story.

GPS is a great tool, my primary navigation tool and i would assume the
primary navigation tool of anyone on a boat. i can't imagine any
reasonable situation where it would ever fail for me. but that doesn't
make understanding when it can fail some kind of crime, it doesn't make
me into some kind of anti-GPS zealot.


Don't forget that tinfoil in your ball cap.


i don't understand why you are being rude to me, i've not done anything
to you.

The ball cap comment was a joke aimed at Da Kine who seems lack a sense
of humour as well.

My comments on jamming are not intended to be rude.

You are being a bit sensitive.

Sorry.

Jeff wrote:
Wayne.B wrote:

On 5 Mar 2006 14:20:24 -0800, "purple_stars"
wrote:


waynes i'm guessing that you mean that the navy doesn't teach RDF, not
that they don't teach celestial. only reason i say that is because it
seems like the military would need backups like celestial because i
understood that the EMP from a nuclear weapons blast could take out
electronics such as GPS systems. is that wrong ?



Yes, it's wrong. They no longer teach celestial.



You keep saying that. However, celestial navigation is shown as part of
the navigation course at the Naval Academy, which is required for many
majors.

The report from a few years ago which created your myth was that
celestial was no longer required for *all* majors.
I am in the Navy. We only teach celestial nav to navigators. In the
past all officers had to learn it and do it. Now you have to learn it
yourself to pass the command exams. It is not taught to everyone.
Almost no-one uses it.

Gary wrote:
Jeff wrote:

Wayne.B wrote:
....

Yes, it's wrong. They no longer teach celestial.

You keep saying that. However, celestial navigation is shown as part
of the navigation course at the Naval Academy, which is required for
many majors.

The report from a few years ago which created your myth was that
celestial was no longer required for *all* majors.

I am in the Navy. We only teach celestial nav to navigators. In the
past all officers had to learn it and do it. Now you have to learn it
yourself to pass the command exams. It is not taught to everyone.
Almost no-one uses it.

I was talking about the US Naval Academy, where they certainly teach
it. Also, you're saying that celestial is required by the Canadian
Navy for command posts; this seems more significant than whether they
teach it.

Of course no one actually uses celestial, other than as an occasional
novelty. However, even a few hours exposure to it is enough for some
students to learn the basics, such as the meaning of a Noon Sight.

Gary wrote in
news:uuQOf.109032$B94.27750@pd7tw3no:


And how did you check the error on that deck watch? Radio? What was
the error and how much does it change daily? Can't just do the time
check anymore. Damn lightening.



Most watches/clocks are fairly consistent in their rate of error.
Prior to your loss of electronics you would have/should have been
maintaining a log of the watch/clock you would use for this type emergency
so that you would know not only it's error but daily rate.
You apply this error and daily rate to your calculations.

otn

Wayne.B wrote in
news
On Mon, 06 Mar 2006 05:01:05 GMT, otnmbrd
wrote:

Gee, I wonder how I navigated all over the world, offshore, prior to
GPS, if I had no viable alternative to GPS.

Probably celestial and DR unless you were lucky enough to be on a ship
with a good inertial system.

Tell us about the times when you couldn't get a celestial fix because
of clouds.



First off remember..... you're offshore. Although it's great to know
exactly where you are at all times, for much of your trip it's not really
necessary and even when things were great for celestial you only got three
"exact" fixes every day ... morning/evening stars and noon.
Sure there are times when you don't get a fix for extended periods and
anyone can tell of cases where this caused a grounding, etc., but for the
most part you were and are able to use your knowledge of your boat's
reaction to weather, known currents, etc. to maintain a reasonable DR until
you do get a sight, come on soundings, approach land, etc.
You use whatever is there.
The problem with the sole reliance on GPS or multiple GPS is that you
become a "mechanical" navigator and either forget how to use other methods
or never learn them to begin with, which can rear up and bite you on the
butt when the bananas hit the fan.

otn

some guys love to be dumb. Some are so dumb they don't even know they
are