Len wrote in news:0bbc5bca-ddfd-4d62-bc81-
:
I'm sure the transmitting power of the ssb wil fry it.
You are correct. One second of SSB and you'll see smoke rising from the
receiver's front end amp.
We could build a low pass filter rolling off around the bottom of the
broadcast band that would pass signals below, say, 600 Khz, blocking
signals above that, but applying 150 watts directly to it would require a
LOT of sections to attenuate the signal to a reasonable level the NAVTEX
receiver could tolerate. I don't know of one available, sorry.
The idea of the automatic relay to disconnect the NAVTEX antenna during
transmissions has another problem. As far as the two receivers are
concerned, the NAVTEX receiver is a short to ground of the HF
signal....and the HF receiver is a dead short for NAVTEX signals.
Putting them in parallel won't make everything dead, but it will reduce
receiver sensitivity a lot in poor conditions.
So, instead of all this backstay nonsense, let's take a more sane
approach separating the two.....
Look at your AM pocket radio...AM only. It operates in this frequency
range. See any huge long protruding antenna? No? It can pick up
stations at night 500 miles away! It does this with a much QUIETER,
noisewise, antenna that is narrowly tuned by a capacitor hooked to your
tuning knob called a loopstick, a coil of wire wound around a ferrite rod
to increase the inductance and sense the RF's magnetic field.....instead
of the backstay's electric field loaded up with STATIC from every
lightning storm within 500 miles on 518Khz. Loopstick antennas are much
better for LF and VLF reception besides being much smaller.
Lucky for you they are available for NAVTEX!
http://www.marinemegastore.com/produ...-Antenna-Unit-
SMG_523_NAVANT.htm
I don't know why most all the dealers are in Europe, England in
particular, but I suspect it's because they don't sell well to Americans
with internet on their phones and boats looking for graphics of the
weather.
This antenna, and Furuno has one like it I think, is a loopstick tuned
specifically for 518 Khz (it'll pick up 490 Khz, too, as that's close)
which will NOT pickup HF transmitters like your SSB and feed them to the
NAVTEX receiver. There's a handy handrail mount, if you like, and they
are both quite cheap.
Let's do it better this way....
Back, again, to England, s/v "Whoosh" has a webpage about his with this
antenna:
http://www.svsarah.com/Whoosh/WhooshPrepNAVTEX.htm
It is very important for good reception that this antenna be mounted AWAY
FROM METAL objects, like your bimini top hardware, light fixtures,
electrical wires that radiate NOISE on low frequencies, as far away as
possible from metal objects that will detune it and grab away its signal.
LF doesn't need altitude, by the way, because its signals come in from
very high up, reflected off the ionosphere when the sunspots return and
feed us more ions...making LF and HF work, again. There are no sunspots
now, in quite a while!
http://www.spaceweather.com/
http://www.hamradio-online.com/propagation.html
http://www.ae4rv.com/tn/propflash.htm
http://ecjones.org/propag.html
http://www.radio-electronics.com/inf...tion/index.php
http://areps.spawar.navy.mil/
Navy SPAWAR's propagation branch has great software the taxpayers paid
for for download. Click on SOFTWARE DOWNLOAD to go to the page, if
you're interested. SPAWAR used to be called NAVELEX and is the Navy's
electrical engineer bureaucracy that makes it all happen...(c;
It's about 6 miles from my house, one of SPAWAR's centers...
Get the proper antenna....SAVE THE RECEIVER - GET LESS STATIC!!