tony wrote in :

We are in the throes of considering fitting a Navtex
receiver but having been warned the air generator we have
fitted could cause havoc with Navtex reception. I held a
portable radio in the vicinity of the generator tuned as
close as it would allow to the Navtex frequency (540 kHz).
Whilst there was no interference from the generator there
was considerable pick up from the Simrad IS15 instruments,
which appears to be emitting from the instruments
networking (Roblink) cabling. Disconnecting the NMEA made
no appreciable difference to the interference being
detected by the radio. The interference is being received
if within 6 foot of anything metal on the boat.
Mast, rigging, guard rails, keel and any wiring. As far as
could be determined with a simple radio the interference
extended up to about 3 MHz.



Unfortunately for everyone, some idiot decided NAVTEX should be in the 200
Khz range where every piece of modern electronics makes an amazing array of
beeps, boops, bzzt..bzzt..bzzt noises with ranges far enough so you can't
possibly get the antenna far enough away from it. Your laptop computer is
a GREAT Navtex jammer, as are all your plastic-cased NMEA electronic
wonders. The big pulse generators in solid-state marine refridgeration, AC
inverters, electronic/computer-controlled battery chargers like the stupid
Guest 10/10 under Lionheart's aft cabin bunk, are also great jammers for
LF, MF and HF way up above CB band!

A loopstick antenna greatly reduces induced noise. Unfortunately, NAVTEX
receivers usually have open wire/backstay type antennas. We're using a ham
receiver. It doesn't have a loop antenna, either.

The only solution I know of is to shut down everything making noise, try to
copy NAVTEX to get what you want, then crank it all back up again for
another fix.....You don't REALLY have to run all that crap at sea 24/7 to
have navigation at 8 knots, you know...(c;

NAVTEX at the dock in the buzzing noises of the marina are
impossible....unless you can shut down the main breaker to the whole
marina, that is. City Marina in Charleston covers up the whole HF band,
too!....even after I've shut down that damned Guest battery
charger/broadband transmitter. It makes more noise on HF than the
Woodpecker OTH radar, HAARP's gigawatts and a thunderstorm overhead!

By the way, that rhythmic bzzt...bzzt...bzzt.bzzt.bzzt on Channel 16 VHF is
your Adler Barbour 12V fridge cold plate. Been there, heard
that...designed by idiots.

--
Larry