Re: Ping Larry - Ferrites?
- From: Larry <noone@xxxxxxxx>
- Date: Sun, 27 May 2007 15:09:33 +0000
Peter Hendra <peter.hendra@xxxxxxxxx> wrote in
I have installed my new Icom, AT130 Antenna tuner and Pactor usb
Unfortunately I could not avoid the wires from the winmd generator
base and the wire from the ATU to the backstays coming to with a foot
of each other.
If the wires are in parallel, that's bad, really bad. RF will couple
from the antenna wire, which is a part of the antenna, itself, onto the
wind gennie wires, going to waste, not on the air. If the wires are
perpendicular to each other, this won't happen. Can you reroute the wind
generator wiring so it is not parallel with the wire going from the tuner
to the backstay, the RF hot wire? Just get them as far away and as
perpendicular to each other as you can get them. Everything on a boat
antenna is a great, big compromise.
Pactor modem works well and power output etc is excellent but I don't
know where to fit all the ferrites you mention. I have a few that fit
smaller cables but none of the size to fit over the coax.
RF will follow the outside of the coax shield, induced by the RF
radiating from the nearby antenna, back towards the radio. But, if it
causes no problem, let's not make one. On the air, RF interference into
a microphone circuit sounds like a rasping sound every time you start
talking. If it gets too bad, it'll go into wild oscillation making a
screaming noise in the transmitter's audio input, but, obviously these
aren't happening so I don't think you have a problem. If it gets into
any kind of modem, it simply won't connect to anyone. Yours works, so is
Ferrites don't need to be tight to the wire, just surrounding them. On
power leads, I use those square ferrites you can take several turns of
power lead wire around, filling it with wire. This also helps reduce
noise RF following the DC and control cable "antennas" back into the
radio receiver, as well as transmitter. Do these as close to the radio
as practical. As to the coax, RG-58 or 6, make an air inductor out of
it. Instead of cutting the coax as short as possible, leave extra on the
radio end and make a smooth, 8-10 turn loop in it about 15cm in diameter,
taping the loop so it will stay tight. The RF inside the coax is
unaffected. The RF sneaking back down the outside sees this series
inductance and is "somewhat" blocked. It reduces the backfed RF to
acceptable levels, even RF that's tearing up mic audio amps.
Another great way to both eliminate RF feedback down the coax and greatly
reduce the radio being destroyed by a static discharge from a nearby
lightning hit, is to route the coax to the engine block. Most backstay
antenna tuners are right over the rudder, inside a locker that's exposed
to the engine compartment. I like to route the coax to a coaxial surge
suppressor mounted in a little stainless (if possible) plate I can bolt
to any engine bolt I can get to. The surge suppressor will trigger on
any static high voltage pulse inside the coax, saving the transmitter,
but not the tuner, of course. This also bleeds any RF following the
cable back to the nav station instruments off to the engine block
(ground) so the coax from that point to the radio is nearly RF free. I
do the same thing to antenna cables on ham radios at home. I route the
coax down the tower, through surge suppressors mounted into a large
aluminum block firmly U-bolted to an 8' electrical ground rod in the soil
next to the tower, one of 3 that also ground the tower. This keeps RF
and lightning from looking in my hamshack for a ground path. I use a 20
turn coax "inductor", just like I described above, to make extra
protective inductance in series to reduce the risk even further. It's
worked for me since the 1960s with good success...(c; One hit blew the
top off the tower and just vaporized the coax back to my ground plate.
The coax and radios on the house side of that plate were untouched! Too
bad the beam antenna and top 3 feet of the tower were also vaporized,
just disappeared. All I remember is a blinding pink flash you'd expect
from a nuclear detonation and being deaf for days after the event....
I would much appreciate your help - once again.
Being back in the water again out of a hot and dirty yard is just
bliss. Using and having to pump your own toilet (- dismantling it due
to a blockage first), going to and fro by dinghy, rocking of the boat
and using the kerosene stove instead of an electric hot plate is like
being in heaven.
You can always tell a true sailor from the rest by just looking at their
faces at the dingy dock, especially if its windy enough to get them wet
on their way in from the anchorage...(c;
Just have to tune the rigging and I am off. All the little things that
need to be completed after a refit can be done under way.
Congratulations! Glad you're at sea, again.
It's always better to be standing on the dock, wishing you were at
Than to be at sea, wishing you were on the dock....
- Ping Larry - Ferrites?
- From: Peter Hendra
- Ping Larry - Ferrites?
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