Doug wrote:
"Jack Painter" wrote in message
news:SR2tc.76990$pJ1.75446@lakeread02...

"Steve (another one)" wrote in message
...
1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for

RF.

Never improvise with something such as spark plug wires.

2.(a) Grounding: RF

This does not have to be wide surface area copper, but doing so will not
hurt, and it will allow the combination-use of the RF ground connection to
serve as a lightning protection ground. RF ground does not require a dc-
connection to ground, and is often designed to use capacitive coupling to
ground for sailing vessels and other marine applications where isolation

for

galvanic protection is adviseable.



NO NO NO coax from ATU to antenna, even inside a metal ship! Use GTO wire.
In an emergency repair in the Aleutians I used HV cable from a television
flyback transformer to the CRT anode once and it worked until the ship got
back to civilization. I have corrected many poor performing backstay
installations by replacing RG-8, 214, etc coax running from the ATU to the
backstay with GTO. What a difference in receive and transmit performance.

Use the widest copper foil you can find, at least 3" for the RF ground path.
The wider the better! Smaller sizes and round wire is too high impedance for
proper HF RF grounding.

Flat braid may be used is you have to use it, putting more that one flat
braid in parallel usually helps.
Doug K7ABX


Thanks for these comments, sorry if was a FAQ, I did search first. I
have since asked the same question of Icom UK and their suggestion was
to use the centre conductor of RG213u - having stripped off the outer
shielding. Someone else told me they cut back the centre conductor of
RG213u and used only the shielding which seems very odd as it would have
little insulation.

Anyway, thanks again, I think I now understand the issues and can
assemble something.

Steve

http://www.shipstore.com/ss/html/ANC/ANC150110.html

"Jack Painter" wrote

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.

"Meindert Sprang" wrote in message
...
"Jack Painter" wrote in message
news:SR2tc.76990$pJ1.75446@lakeread02...

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for
RF.

Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about
200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz)
antenna
connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.

Hi Meindert, I don't understand your reasoning there, sorry. And Doug too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same Sunair
ATU that I use, connected to the wire HF antennas. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to a
insulated backstay of a sailboat.

Best regards,

Jack Painter
Virginia Beach,VA

In article SR2tc.76990$pJ1.75446@lakeread02,
"Jack Painter" wrote:

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for RF.
Never improvise with something such as spark plug wires.


Bzzzt, Wrong answer, would you like to try for what's behind Door No. 3??


Coaxial Cable is the WRONG Stuff to be feeding and EndFeed Longwire
Antennas with, even should you not ground the shield, which would be
disasterous in any case.
What is needed is good old GTO15, which like others have
plainly stated, High Voltage - Super High Isulation Wire. In a pinch
I have used the Center Insulation and Feedwire from RG8 or similar
coax with the shiled and jacket stripped off, but this is still not as
good as GTO15.
Yes there are a bunch of Installers who ran around using Hardline
to feed USCG MF/HF SunAirs Antenna Systems from their AutoTuners a few
years back, but the folks who had to maintain those systems 24/7 up
here in alaska, ripped all that **** out and replaced it with
conventional PhospherBronze Antenna Wire with insulators, when it was
determined that the original installations were STONED DEAF compared to
a one transistor radio.
How do I know this you ask? I was the FCC Resident Field Agent
for Southeastern Alaska, and watched it all happen.


Bruce in alaska
--
add a 2 before @

"Bruce in Alaska" wrote in message
"Jack Painter" wrote:

who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same
Sunair
ATU that I use, connected to the wire HF antennas. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to
a
insulated backstay of a sailboat.

Coaxial Cable is the WRONG Stuff to be feeding and EndFeed Longwire
Antennas with, even should you not ground the shield, which would be
disasterous in any case.
What is needed is good old GTO15, which like others have
plainly stated, High Voltage - Super High Isulation Wire. In a pinch
I have used the Center Insulation and Feedwire from RG8 or similar
coax with the shiled and jacket stripped off, but this is still not as
good as GTO15.
Yes there are a bunch of Installers who ran around using Hardline
to feed USCG MF/HF SunAirs Antenna Systems from their AutoTuners a few
years back, but the folks who had to maintain those systems 24/7 up
here in alaska, ripped all that **** out and replaced it with
conventional PhospherBronze Antenna Wire with insulators, when it was
determined that the original installations were STONED DEAF compared to
a one transistor radio.
How do I know this you ask? I was the FCC Resident Field Agent
for Southeastern Alaska, and watched it all happen.

Bruce, I am asking why there is apparently such difference between feeding
an ungrounded dipole with coax from an ATU (my shore station) and feeding an
insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback
in the summertime with that setup and I just can't understand what GTO-15
does that hardline doesn't. If you could explain or reference a document
that specifies the reasoning I would try to correct my misunderstanding.

Thanks,

Jack Painter
Virginia Beach, Va

Bruce, I am asking why there is apparently such difference between feeding
an ungrounded dipole with coax from an ATU (my shore station) and feeding
an
insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback
in the summertime with that setup and I just can't understand what GTO-15
does that hardline doesn't. If you could explain or reference a document
that specifies the reasoning I would try to correct my misunderstanding.

Thanks,

Jack Painter
Virginia Beach, Va

If I can jump in, the quick answer is that the coax is approximately the
same impedance as the center of your ungrounded dipole, at least at the
frequency for which it is resonant. Thus, from the perspective of the
transmitter and the antenna, the transmission line is "invisible." I'm
exaggerating, of course.

In the case of a backstay used as an antenna, the feedpoint impedance can be
anywhere from a small fraction of an ohm at low frequencies to thousands of
ohms where it approximates a half-wavelength. In those cases, the coax will
most certainly not be invisible and will most likely either burn up or
greatly attenuate your signal (incoming as well as outgoing, actually).

If you tried to end-feed your half-wavelength dipole with coax, you would
see a similar problem because the impedance at the ends is in the thousands
of ohms range.

Hope that helps.

Chuck

"Jack Painter" wrote in message
newsxstc.52$9h.43@lakeread02...

Hi Meindert, I don't understand your reasoning there, sorry. And Doug
too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same
Sunair
ATU that I use, connected to the wire HF antennas.

A backstay antenna is relatively short compared to the wavelength. It
therefore has a high impedance. To match it to the 50 ohm of the
transceiver, the impedance has to be transformed by an L-circuit with the
capacitance at the low impedant side to ground and the inductance from the
low impedance "hot" side to the antenna. If you would use coax at the high
impedant antenna side, you get a terrible mismatch. The capacitance of this
pice of coax adds to the L circuit at the wrong side, effectively giving you
a PI circuit which is unable to match the high impedant backstay to the 50
ohms of the transceiver.

It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners.

Theoretically no. But your land dipole is probably much longer than a
backstay and therefore has a lower impedance. By the way, does your coax
connect directly to the dipole or do you have a balun (with a possible
impedance transformation wich makes the coax have less influence)?

Meindert

"Meindert Sprang" wrote in message
...
"Jack Painter" wrote in message
newsxstc.52$9h.43@lakeread02...

Hi Meindert, I don't understand your reasoning there, sorry. And Doug
too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same
Sunair
ATU that I use, connected to the wire HF antennas.

A backstay antenna is relatively short compared to the wavelength. It
therefore has a high impedance. To match it to the 50 ohm of the
transceiver, the impedance has to be transformed by an L-circuit with the
capacitance at the low impedant side to ground and the inductance from the
low impedance "hot" side to the antenna. If you would use coax at the high
impedant antenna side, you get a terrible mismatch. The capacitance of
this
pice of coax adds to the L circuit at the wrong side, effectively giving
you
a PI circuit which is unable to match the high impedant backstay to the 50
ohms of the transceiver.

It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners.

Theoretically no. But your land dipole is probably much longer than a
backstay and therefore has a lower impedance. By the way, does your coax
connect directly to the dipole or do you have a balun (with a possible
impedance transformation wich makes the coax have less influence)?

Meindert,

Thanks very much, that was a lightbulb going off (duh) that the backstay on
less than a 70' yacht is going to have a seriously short antenna WRT
wavelength! My wires and dipole are of course half wave devices and at
desired frequencies do not even require a tuner at all. And yes I do use a
1:1 Balun (isolation only on the tunes dipole, 4:1 on random wires). And
just because the specs of my Sunair Coupler _could_ deal with any wire 30'
or longer, that would be a frivolous effort to try to tune, say 2182khz on
so short a wire with 50ohm coax. It does work mediocre on an 80' wire but I
am still somewhat surprised that any sailing vessel could get much
performance (if any do) on MF from a (relatively short) backstay antenna.
Closer to the 1/2 wavelength, I would think that coax would be more
appropriate to the ATU-to-Antenna match than this GTO-15. Correct? And a 4:1
balun would in other cases make the match even more feasable, as well as the
desirable electrical isolation from noise that a Balun can provide.

73

Jack Painter
Virginia Beach, Va

"Chuck" wrote in message ...
Bruce, I am asking why there is apparently such difference between
feeding
an ungrounded dipole with coax from an ATU (my shore station) and
feeding
an
insulated (hence ungrounded) backstay from an ATU? I work Alaska
bareback
in the summertime with that setup and I just can't understand what
GTO-15
does that hardline doesn't. If you could explain or reference a document
that specifies the reasoning I would try to correct my misunderstanding.

Thanks,

Jack Painter
Virginia Beach, Va

If I can jump in, the quick answer is that the coax is approximately the
same impedance as the center of your ungrounded dipole, at least at the
frequency for which it is resonant. Thus, from the perspective of the
transmitter and the antenna, the transmission line is "invisible." I'm
exaggerating, of course.

In the case of a backstay used as an antenna, the feedpoint impedance can
be
anywhere from a small fraction of an ohm at low frequencies to thousands
of
ohms where it approximates a half-wavelength. In those cases, the coax
will
most certainly not be invisible and will most likely either burn up or
greatly attenuate your signal (incoming as well as outgoing, actually).

If you tried to end-feed your half-wavelength dipole with coax, you would
see a similar problem because the impedance at the ends is in the
thousands
of ohms range.

Hope that helps.

Chuck, as with Meindert's answer, yes that helps, thank you.

I do end-feed a long wire as I said earlier, but it uses a 4:1 Balun, and
additionally, has one side of that Balun shorted to ground. This is a
noise-limiting design, and while the nice folks at Radio Works (Portsmouth,
Va) maintain that it cannot possibly work this way (their Baluns), the CG
aircraft I worked in Ecuador with it thought otherwise. So does it's
designer, whose name slips my mind at the moment but he was a primary
contributer to "Proceedings", and a Phd in EE with many patented antenna
designs. Anyway, it would be interesting to see some modelling done with
backstay antennas using various feedline approaches. I suspect the
difference varies greatly with wavelength, height above ground (water),
angle, and frequency.

73,
Jack Painter
Virginia Beach, Va

On Fri, 28 May 2004 18:58:25 -0400, "Jack Painter" wrote:


good stuff by Meindert snipped

Thanks very much, that was a lightbulb going off (duh) that the backstay on
less than a 70' yacht is going to have a seriously short antenna WRT
wavelength! My wires and dipole are of course half wave devices and at
desired frequencies do not even require a tuner at all. And yes I do use a
1:1 Balun (isolation only on the tunes dipole, 4:1 on random wires). And
just because the specs of my Sunair Coupler _could_ deal with any wire 30'
or longer, that would be a frivolous effort to try to tune, say 2182khz on
so short a wire with 50ohm coax. It does work mediocre on an 80' wire but I
am still somewhat surprised that any sailing vessel could get much
performance (if any do) on MF from a (relatively short) backstay antenna.
Closer to the 1/2 wavelength, I would think that coax would be more
appropriate to the ATU-to-Antenna match than this GTO-15. Correct? And a 4:1
balun would in other cases make the match even more feasable, as well as the
desirable electrical isolation from noise that a Balun can provide.

73

Jack Painter
Virginia Beach, Va


Jack, I too wonder about the matching of (short) backstay HF antennas.
The thing that occurs to me is that trying to match the ATU to the antenna
isn't really the goal. The ATU *IS* the matching network. By feeding the
backstay with a coax, the excess capacitance (due to the coax) is just
another reactance the ATU must try to "tune out". Using coax is equivalent
to conncting shunt capacitors from there to ground.
My opinion is that the lead, whatever it is, between the ATU and the
*real* antenna, becomes part of the antenna. To me it makes sense
to use something like GTO-15 between the ATU and backstay.
We also must remember that matching the ATU to the backstay is only
part of the job. The ATU must present a proper impedance to
the transceiver. If the antenna is a horrible match, and the ATU
runs out of "range", then the impedance presented to the transceiver must
suffer also.
Be nice to put a network analyzer on a backstay and see what it
really looks like, eh? Be an opportunity to experiment with
different grounding schemes also. I'm convinced that salt water
is the best possible ground....coupling/connecting to it is the challange.
My 2-bits worth...
Norm B