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

--
http://sailsugata.com s/v Sugata Hans Christian 38 Mark II
http://windandtides.com San Francisco Sailing Weather
http://gearandboats.com Free San Francisco Boating Classifieds

On 25 Mar 2007 10:06:08 -0700, "thuss" wrote:

"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."

Lets just say that you should not use coax for the antennal lead since
the lead becomes part of the antenna and you want it to radiate. It
does need to be insulated however to prevent RF burns to those in the
cockpit. There is special wire made for that purpose which you should
be able to get at your local marine electronics dealer, but in a pinch
you could take some large coax cable like RG-8 or RG-11, strip off the
outer insulating jacket and coper braid, leaving only the insulated
center conductor.

Thanks for clarifying Wayne. I had a look and it appears as if West
Marine carries the correct cable called GTO 15 made by Ancor:

http://www.westmarine.com/webapp/wcs...-1/10001/22784

I'll be curious to see how this effects my HAM radio performance since
the original installation had coax as the feedline!

Thanks,
Todd

--
http://sailsugata.com s/v Sugata Hans Christian 38 Mark II
http://windandtides.com San Francisco Sailing Weather
http://gearandboats.com Free San Francisco Boating Classifieds

On Mar 25, 11:58 am, Wayne.B wrote:
Lets just say that you should not use coax for the antennal lead since
the lead becomes part of the antenna and you want it to radiate. It
does need to be insulated however to prevent RF burns to those in the
cockpit. There is special wire made for that purpose which you should
be able to get at your local marine electronics dealer, but in a pinch
you could take some large coax cable like RG-8 or RG-11, strip off the
outer insulating jacket and coper braid, leaving only the insulated
center conductor.

wrote in news:1174870222.221326.262340
@n59g2000hsh.googlegroups.com:

I'll be curious to see how this effects my HAM radio performance since
the original installation had coax as the feedline!



It won't help. Boats running low power (150W) and end-fed, untuned short
wire antennas have SUCKY signals, no matter what you do....especially on
the lower HF bands. A 55' backstay, between the insulators, is an
antenna at 8.5 Mhz, if you have a good ground on the tuner (1/4
wavelength) and a great 1/2 wavelength antenna at 17 Mhz, where it
doesn't even need a ground system to work against. At any other
frequency band, especially below 8 Mhz, the antenna is way too short to
fit the RF wave onto and the lower you go the worse it gets. Between 8.5
and 17 Mhz, the antenna is a complex impedance with a lot of inductive
reactance. The wave doesn't fit well the further away from 8.5 and 17
Mhz you get, killing its radiating potential.

Use 468/ft length = Mhz to determine what resonance is for your backstay.
It'll work fair there on 150W. Far away from there in frequency, it'll
suck, just like everyone else's. Hams use resonant antennas for a
reason...(c;

Larry
--
Message for Comcrap Internet Customers:
http://tinyurl.com/3ayl9c
Unlimited Service my ass.....(d^

"Larry" wrote in message
...
wrote in news:1174870222.221326.262340
@n59g2000hsh.googlegroups.com:

I'll be curious to see how this effects my HAM radio performance since
the original installation had coax as the feedline!


It won't help. Boats running low power (150W) and end-fed, untuned short
wire antennas have SUCKY signals, no matter what you do....especially on
the lower HF bands. A 55' backstay, between the insulators, is an
antenna at 8.5 Mhz, if you have a good ground on the tuner (1/4
wavelength) and a great 1/2 wavelength antenna at 17 Mhz, where it
doesn't even need a ground system to work against. At any other
frequency band, especially below 8 Mhz, the antenna is way too short to
fit the RF wave onto and the lower you go the worse it gets. Between 8.5
and 17 Mhz, the antenna is a complex impedance with a lot of inductive
reactance. The wave doesn't fit well the further away from 8.5 and 17
Mhz you get, killing its radiating potential.

Use 468/ft length = Mhz to determine what resonance is for your backstay.
It'll work fair there on 150W. Far away from there in frequency, it'll
suck, just like everyone else's. Hams use resonant antennas for a
reason...(c;

It might help, and shouldn't hurt. Larry, the reason ham use resonant
antennas is because they can. All things equal, a resonant antenna will
perform better, because there will be less loss in matching networks, ground
systems, feedline loss, etc.

HOWEVER, on a boat (on *my* boat, anyway), puttiing up, and keeping up, a
resonant antenna for all the frequencies I regularly use is too much of a
nuisance. I have an insulated backstay antenna, about 50 ft long, and a
pretty good ground system. I have an Icom AT-130 tuner right below the
backstay, with a short length of high-voltage (GTO-type) wire from the tuner
to the backstay. There is a wide copper strap from the ground system to the
tuner. The radio is an Icom 710-RT. This is a pretty standard
installation, and it works very well.

I'm sure it could work better, but it during last summer's race from San
Francisco to Hawaii, and our trip back, we were participating in a
marine-band net once or twice a day. VALIS (my boat) typically had one of
the best signals out there, on 6 and 8 MHz. Yesterday, I had re-installed
the radio after some maintenance, and my first radio-check contact was on 20
Meters with a ham in the Carribean -- I was in San Francisco. My point is
that it works well enough. Yeah, it isn't as good on the lower frequencies
as a full-length antenna would be. A different installation may be better,
but so would a tri-band yagi at the top of my mast. I'm happy to stick with
what I have.

As has been mentioned, using coax from the tuner to the end of the backstay
has two disadvantages: It adds shunt capacitance, and some loss, which can
makes the tuner's job more difficult. Also, it may arc through from the
center conductor to the shield, during operation at certain frequencies
where the voltage can rise to very large values.

(Larry, and anyone else interested -- I will be asking a question about
Raymarine vs Furuno nav systems, and would appreciate some advice. I will
start a new thread over in rec.boats.electronics so I don't hijack this
one.)

- Paul (wb6cxc)
- S/V VALIS -- PSC44 #16 -- Sausalito, California
- www.sailvalis.com

Paul wrote:
SNIP
As has been mentioned, using coax from the tuner to the end of the backstay
has two disadvantages: It adds shunt capacitance, and some loss, which can
makes the tuner's job more difficult. Also, it may arc through from the
center conductor to the shield, during operation at certain frequencies
where the voltage can rise to very large values.

SNIP
- Paul (wb6cxc)
- S/V VALIS -- PSC44 #16 -- Sausalito, California
- www.sailvalis.com



Hello Paul,

Part of the problem in analyzing a run of coax between the tuner and the bottom of the backstay is agreeing on what the alternative is. If the alternative is having the tuner right at the base of the backstay, then that will usually give the best results. (But see below)

But if the tuner is, say eight (or more) feet away from the bottom of the backstay and the run is more or less along the waterline, then that's not going to be a very attractive alternative. On frequencies where that length constitutes a current node, (especially at higher frequencies where the antenna might be a short, automotive-type whip) that length is an important part of the radiating system. But its radiation is essentially into the water where it does no good.

A variation on that is where the connection between the tuner and the "ground" is several feet long: a not unusual arrangement. In that case, the antenna actually begins at the ground system and the ground wire running to the tuner is a full, radiating part of the antenna!

So the rules are not just to avoid coax between the tuner and the backstay, but to install the tuner as close to the backstay as possible and to install the ground system as close as possible to the tuner. Fortunately, these rules are tempered with the knowledge that many installations work acceptably despite their departures from the ideal. ;-)

I would second Bruce's recommendations, and also point out that on the Chesapeake and its tributaries as well as on the Great Lakes, you will need to provide lots of area for your RF ground because of the water's lack of salinity.

73,
Chuck
NT3G

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"thuss" wrote in news:1174842368.471514.316370
@n59g2000hsh.googlegroups.com:

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 initial installation was just WRONG. Coax cable left open on the
backstay end is simply a Faraday Shield the also makes an output
capacitor because of the proximity of the ground (shield grounded) and
the center conductor hot with RF. What SHOULD have been installed was a
high voltage cable on standoff insulators or just hanging out AWAY FROM
ALL METAL OBJECTS...NOT TYWRAPPED TO THE BOTTOM METAL PARTS OF THE
BACKSTAY, PLEASE....

How long is the run from the tuner's antenna output insulator to the top
of the backstay's bottom insulator, the feedpoint of the antenna? The
tuner should be located as close to that point as is practical.
Lionheart's is less than 2' and I use a stainless wire to it.

Every piece of metal sticking up above the deck is a passive part of the
backstay antenna system and can have high voltage points, of a sort, on
them if they are of a resonant length at the frequency you are operating
on. How high depend on their proximity and parallelness to the radiating
element. This is RF, not AC power. At some frequency, all metal
rods/shrouds/masts/anything that conducts becomes resonant because of its
length. Ride by any AM radio station, whos tower is the radiating
element at all of them, and look at the insulators installed in every guy
wire around the tower to make sure each section between those insulators
is NOT a resonant length of wire (too short) which reduces secondary
radiation and absorption to insignificant values.

Now to safety. 150 watts on a marine HF isn't much RF power, relatively
speaking. Stop by Lionheart and I will let you run 150 watts whistling
into its SSB transmitter while I'm wrapped around the backstay antenna,
unharmed. Tower climbers never turn off AM radio stations to climb up
and change the lights, or even those insulators while hanging upside down
from the guy wires they are working on...which scares me to death. You
aren't burned from an high voltage wire AS LONG AS YOU ARE AT THE WIRE'S
POTENTIAL. Where you get into trouble, which is really minimal and not
really dangerous at 150 watts HF, is when you get ACROSS high voltages of
different potentials/phase...where current, which is what burns/shocks,
flows through your body. Don't touch the backstay and boom or mizzen or
that seawater-grounded metal helm wheel when the transmitter is on.

The wire coming from the tuner to the backstay, by the way, is part of
the antenna, which starts at the high voltage insulator on the tuner.


Larry
--
Message for Comcrap Internet Customers:
http://tinyurl.com/3ayl9c
Unlimited Service my ass.....(d^

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

--
http://sailsugata.com s/v Sugata Hans Christian 38 Mark II
http://windandtides.com San Francisco Sailing Weather
http://gearandboats.com Free San Francisco Boating Classifieds


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.......
--
add a 2 before @