In article .com,
"thuss" wrote:

I'm replacing the antenna feed line between my antenna tuner and
insulated backstay. It's currently a coax cable but then I read that
I should use insulated antenna wire and NOT use coax for the antenna
feed line. This raises some questions though, isn't the whole reason
to use coax because it's shielded which prevents the feed line from
radiating and causing RF burns in the cockpit?

The source I read it on is: http://www.geocities.com/bill_dietrich/Radio.html

"from the output terminal of the tuner/coupler you want insulated VERY
high voltage antenna wire (usually about 14 or 16 gauge) led to a
point on your backstay just above the insulator ... You CANNOT use
coax for this part of your antenna lead."

Thanks,
Todd

--
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There have been MANY different Ideas on what type of wire to use for
the connection between an AntennaTuner and an EndFeed MF/HF Wire
Antenna. The Accepted Standard used in Commercial Marine Installations
has always been, GTO-15, which is a Copper Conductor, Insulated to 15Kv,
and shiethed with a very thick Black Vynel Outer Jacket. Some folks
have used coax cable by only using the Shield Braid as the conductor,
but this doesn't have the same 15Kv Insulation qualities. Using Coax
in a Standard Configuration, with the Inner conductor as the Antenna
Connection and a Grounded Shield, or Braid, is a BIG NO-NO, as the shield
would add Significant Shunt Capacitance, that the tuner must deal with,
as well as shunting a significant portion of the RF to Ground. The same
can be said for Tye-Wrapping ANY portion of the Antenna to ANY Grounded
Surface, or even ungrounded surface of a conducting material.

When designing a Effective MF/HF Marine Antenna System, one needs to
Drag Out the Special RF Specticals, and view the vessel thru these,
which will only let the user see those things that have significance in
the MF/HF Spectrum. So lets look, and see what we can see.

First we see the SeaWater. It looks like a Flat Plate of Copper with
the vessels hull sticking out of it, if the hull is made of a Conducting
Material, OR, a Hole in the Copper sheet, where the hull displaces the
SeaWater. Then we see the Engine, Gearbox, Wiring, and all the Grounded
conducting material inside the hull, including any Grounded Stays. On
closer inspection we see the Antenna Tuner connected to the RF Ground
System. Hopefully, this is done with a LOW Impedance connection at MF/HF
Frequencies.

Now if the Hull/House Material is conductive, then we need a RF Feedthru
Insulator, of a size to make as SMALL of Capacative Coupling as possible
to the Antenna Connection between the Antenna Tuner and the bottom of
the EndFeed Wire. Now look at the External side of the RF Feedthru
Insulator, and see that the Antenna Wire stays away from ANY of the
Grounded things that we looked at earlier. The farther the better, but
anything over 6-10 inches should be sufficent. No reason to become ANAL
Retentive on this point.

If the Hull/House Material is non-conductive, then all we really need to
do is see that the Antenna Wire stays away from ANY of the Grounded
things that we looked at earlier. The farther the better, but anything
over 6-10 inches should be sufficent. No reason to become ANAL Retentive
on this point.

Now concerning RF Grounding of MF/HF Marine Antenna Systems, the better
(Lower Impedance) the RF Ground, the BETTER the System will WORK. More
is Better, less is worse. Conductive Hull Material is the BEST, when
a non-conductive material is the case, then ANYTHING that adds to the
Surface AREA of the RF Grounded, is better, and the CLOSER these things
are to the SeaWater, the BETTER. You are building a Capacative Coupling
to the SeaWater, and you make a BIGGER Capacitor (Lower Impedance) by
having MORE surface AREA, and less space between the two plates of the
Capacitor.


:end of MF/HF Marine Antenna Lecture 101

Bruce in alaska I use to give this lecture a lot, but MF/HF Marine
Radio is a very Mature Technology, and soon to
be a DEAD Technology.......
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add a 2 before @