Hi ng,

The boat came with a Fastnet Radio FMD55P navtex-receiver, using a
passive antenna: the insulated backstay via a Balun.
Now I installed a ssb transceiver + tuner and connected the tuner to
the backstay. The navtex receiver is not in use at the moment cause
I'm sure the transmitting power of the ssb wil fry it.

Is there a way to solve this cause I would like to use the navtex
again,.It has no possibility for an active antenna, just passive. I
would like to use the backstay for both now I "heared" about a switch
that immediately switches off the connection to the navtex when it
senses ssb-transmitting, Any thoughts ? Every reaction will be highly
appreciated.

Regards, Len

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!!

The standard method would be to use an rf antenna relay to disconnect
the rx antenna when the ssb is keyed. That's what saves the ssb rx
internally.

The alternative is to use a separate ae for the receiver only
circuit.

Terry K

"Len" wrote in message
...
Hi ng,

The boat came with a Fastnet Radio FMD55P navtex-receiver, using a
passive antenna: the insulated backstay via a Balun.
Now I installed a ssb transceiver + tuner and connected the tuner to
the backstay. The navtex receiver is not in use at the moment cause
I'm sure the transmitting power of the ssb wil fry it.

Is there a way to solve this cause I would like to use the navtex
again,.It has no possibility for an active antenna, just passive. I
would like to use the backstay for both now I "heared" about a switch
that immediately switches off the connection to the navtex when it
senses ssb-transmitting, Any thoughts ? Every reaction will be highly
appreciated.

Regards, Len

A circulator with 25+ dB of isolation will work just fine.

"Larry" wrote in message
...
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.

Not much smoke if its designed properly.



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.

How about a twin T bandpass for Navtex? Do the job just fine!




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.

I wish it were true but it's not.


Putting them in parallel won't make everything dead, but it will reduce
receiver sensitivity a lot in poor conditions.

The spurious emissions will do worse than impedance matching.


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!

Only if they transmit 100 kW EIRP. AM radio sensitivity is around 100 uV. FM
radio is 0.5 uV.


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.

No, no, no! A Faraday antenna is better for noise. Loopsticks are poor
antennas at best.



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.

How can aluminum detune a supposedly "magnetic" antenna?



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.

No, the principle mode is groundwave.


There are no sunspots
now, in quite a while!

Great! Now the global warming alarmists will finally shut up.



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...

Can I get NEC4 from them?



Get the proper antenna....SAVE THE RECEIVER - GET LESS STATIC!!

Just because the antenna are physically isolated doesn't mean they are
electrically isolated. Check the ground paths and do a site survey with the
SSB transmitter on.

In article ,
"Bob Furterona" wrote:

Only if they transmit 100 kW EIRP. AM radio sensitivity is around 100 uV. FM
radio is 0.5 uV.

I don't know what school you went to, but your RF Engineering Degree,
must have come from a Cracker Jacks Box...... Typical AM Broadcast
Field Strength Measurements for Antenna Pattern Contours are done
at 100 uv/Meter, and those levels are a VARY STRONG Signals, and usually
out from the Transmitter site, many miles.

On Thu, 29 May 2008 10:58:08 -0400, "Bob Furterona"
wrote:

No, no, no! A Faraday antenna is better for noise. Loopsticks are poor
antennas at best.

For what it's worth, you can get a better AM signal on a portable
radio by attaching a random length of wire to the end of the FM whip.

Casady

You wrote in news:you-F83814.10500929052008
@netnews.worldnet.att.net:

I don't know what school you went to, but your RF Engineering Degree,
must have come from a Cracker Jacks Box...... Typical AM Broadcast
Field Strength Measurements for Antenna Pattern Contours are done
at 100 uv/Meter, and those levels are a VARY STRONG Signals, and usually
out from the Transmitter site, many miles.



about 180' from the business end of the 3-tower array of WWKB-AM's 50KW
blowtorch in Hamburg, NY is a very nice looking house in a very nice
looking neighborhood lined up exactly with the array....right off the end.

I wonder how they shut down any lights in that house?.....(c;

Field Strength in the living room is in KV/m......hee hee.

I'd like to live there, myself. I'd have an impressive loop on 1520 Khz in
the attic to power all the lighting from rectified RF 24/7/365! Wonder if
anyone makes an AM band resonant water heater??...hmm....

Bet I could bend their pattern....(c;