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

--
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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
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http://tinyurl.com/3ayl9c
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"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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"chuck" wrote in message
...
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.

Chuck,

Completely agree. The conductors leaving the tuner are part of the
radiating antenna, so the orientation will make a difference, and using
shield-grounded coax will only make matters worse. The connection to the
ground also needs to be electrically short -- not just because it is a
radiator, but because the tuner may not function if it's ground is "hot",
and the coax feedline from the radio to the tuner will also be hot.

I was describing my installation because in my opinion it is an example of a
well-installed system. While I've seen some badly-designed boat antenna
systems, mine is hardly unique, and I think that some folks here are being
pessimistic about how well a good insulated-backstay antenna system can
operate. Boats are floating compromises. We do the best we reasonably can,
and that usually takes some education, but we need to recognize when we have
reached our own point of diminishing returns.

-Paul

chuck wrote in news:1174938449_4055
@sp6iad.superfeed.net:

Chuck
NT3G



Chuck, turn on wordwrap on your news client. Each of your paragraphs are
one longggg line...(cx

Larry
--

Larry wrote:
chuck wrote in news:1174938449_4055
@sp6iad.superfeed.net:

Chuck
NT3G



Chuck, turn on wordwrap on your news client. Each of your paragraphs are
one longggg line...(cx

Larry

Sorry about that. Thanks for the heads
up, Larry.

Chuck

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chuck wrote in news:1174968407_4877
@sp6iad.superfeed.net:

Sorry about that. Thanks for the heads
up, Larry.


I nearly fell out of my chair before I got to the end of those lines....hee
hee...(c;



Larry
--