"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

"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 19:10:14 -0400, "Jack Painter"
wrote:

"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


Jack,

Using a balun to feed an end fed wire may help and it may hurt the
situation. It depends on the length of the wire verses frequency.

If the wavelength is greater than a quarter wave length and the
impedance of the wire is high, the balun will transform it down to a
sometimes easier to match impedance. However if you use the antenna on
different bands and you chose a band where the impedance of the
antenna is low, then the 4:1 balun will step the impedance down even
lower than the already low impedance of the antenna. It may well be
that it is too low to match efficiently.

As a general rule that type of balun is not a good idea when using
that type of antenna on multiple bands.

The only good a 1:1 balun would do with that type of antenna would be
to decouple the feed line from the antenna (assuming coax feed line)
and keep the feed line from radiating and or picking up unwanted
signals.

Regards
Gary

In article ulztc.40$Y21.34@lakeread02,
"Jack Painter" wrote:

"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



The fellow that followed your post did a good job in his reply.
The thing that get most of the rookie marine installers in trouble
is that they think of an antenna and tuner as if it only worked
at one frequency. They design the system for that frequency and think
they have a good system. Well it does work for one frequency but when
they try another band, things go very wrong and things just don't work
anymore. This is exactly why tuned counterpoises are an absolute JOKE
in the Marine Radio Service, but we still see them touted as the
greatest thing since canned beans. A good antenna system for a Marine
Radio Installation needs to be as efficent as possible across the whole
MF/HF Spectrum. Given a Wood or Plastic hull, this is a very daunting
challenge for the worlds best RF Engineer, let alone the SuperHam turned
Instant Expert Marine Radio Installer in a day. What is required is:
1. The Best RF Coupled Ground system one can afford to install onboard.
2. No compromise on the RF Ground System.
3. It is the RF Ground that makes the Radio work.
4. An antenna that is long enough to have a reasonable antenna
effeicency at the lowest frequency that the radio will operate at.
(this means about 75 Ft or more for 2182 Khz)
5. No compromise on the installation because of the wifes astetic
senseabilities. (build it to work, not just look good)
There are more but I think you get the idea. Just because you can
get a signal report on 12 Mhz during the day from the other coast
doesn't mean squat, about how good your Radio system is really doing.
If the band is open a 10watt TX on a dummyload can be heard on the other
coast. What makes a good system is carefully planning the installation
of the RF Ground System and then not compromising the antenna length
because you can't figure out how to install what is needed to make the
system work. All autotuners did for the industry is allow any fool to
install something that looks good, but radiates about as well as a wet
noddle. Back when all the tuners were setup by the installing Tech, he
had to actually make the system work, or he didn't get paid. Now there
is a novel thought.

Ok now I'll get off my soapbox......

Bruce in alaska
--
add a 2 before @

All --

Please comment on the following:

What about using copper tubing as an RF ground connection? Since the
current flows on the surface, a tube seems to be the most space efficient
way to get a large surface area. PI*R seems to say that a 1" copper tube
would be as effective as a 3" or so copper foil.

Any thoughts?

Thanks,
Dave.

"Bruce in Alaska" wrote in message
...
In article ulztc.40$Y21.34@lakeread02,
"Jack Painter" wrote:

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

Major snippage

Did you ever try to route copper tube through all the nooks and almost
inaccessible places that you have to run the foil in a boat in order to
connect the radio, antenna tuner, and dyna-plate? I can form a coat
hanger to stick through a small crack, tape it to the foil and pull the
foil through the crack. Can you do that with copper tube. Copper tube
may give the same surface area, but installation on most boats would be
a nightmare.
Kelton
s/v Isle Escape

Dave Morschhauser wrote:
All --

Please comment on the following:

What about using copper tubing as an RF ground connection? Since the
current flows on the surface, a tube seems to be the most space efficient
way to get a large surface area. PI*R seems to say that a 1" copper tube
would be as effective as a 3" or so copper foil.

Any thoughts?

Thanks,
Dave.

"Bruce in Alaska" wrote in message
...

In article ulztc.40$Y21.34@lakeread02,
"Jack Painter" wrote:


"Bruce in Alaska" wrote in message

"Jack Painter" wrote:

Major snippage

This addresses a question I thought I saw on this group not long ago. I
apologize for not being able to post this in a timely way. I also apologize
if this information has already been posted.

The question was whether it was necessary to provide an RF ground for the
transmitter in addition to the RF ground provided at the ATU. I believe the
answer is generally no.

First, whether there is any direct connection between the transmitter case
(i.e., the outer shield of the coax connecting the transmitter to the ATU)
and the ground terminal at the output of the ATU is entirely coincidental.
Well, not really coincidental. It would be better to say that such a direct
connection is not required. A good many ATU designs utilize inductive
coupling to the transmitter, or to the antenna, and a direct connection in
those cases is purely optional.

The common marine ATUs, however, rely on a form of L-matching circuit in
which there IS a direct connection between input and output "grounds". And
so the transmitter case winds up being connected directly to the ATU ground
terminal and, therefore, to the vessel's RF ground system, whatever that
might be.

We need to keep in mind that the proper functioning of an antenna, tuner,
transmission line, and transmitter, whether on a boat or off, does not
require as a matter of theory that the transmitter case be connected to RF
ground.

As a practical matter though, the transmitter and the transmission line to
the tuner are both in the very near field of the antenna. This is especially
true on a boat. RF from the antenna can travel along the outer shield of the
coax, along microphone, speaker, and power cables and get back inside the
transmitter with difficult-to-predict consequences!

Getting to the real point, now. So sometimes, we need to do things like run
a copper foil (low impedance) RF ground connection from the transmitter case
to the boat's RF ground system. Sometimes it will help, sometimes it can
make matters worse. Sorry. Also, the system is likely to behave differently
at different frequencies. There are ways to test for these currents and
often ferrites can be used in the lines to choke problem currents.

Finally, caution should be exercised in relying on copper foil to provide
lightning protection. It would vaporize like an old-fashioned fuse with any
significant current flow. It would be fine, however, for draining off charge
accumulations from masts and wire rigging.

Hope this helps.


Chuck

"Chuck" wrote in message ...
This addresses a question I thought I saw on this group not long ago. I
apologize for not being able to post this in a timely way. I also
apologize
if this information has already been posted.

The question was whether it was necessary to provide an RF ground for the
transmitter in addition to the RF ground provided at the ATU. I believe
the
answer is generally no.

The best place for grounding is at the ATU. Grounding the TX is not
necessary then. If you only ground the TX, high RF currents will flow on the
outside of the coax from ATU to ground and as a result the coax will radiate
too.

Meindert
PE1GRV

In article ,
"Meindert Sprang" wrote:

The best place for grounding is at the ATU. Grounding the TX is not
necessary then. If you only ground the TX, high RF currents will flow on the
outside of the coax from ATU to ground and as a result the coax will radiate
too.

Meindert
PE1GRV

One small caveat that I would make to the above is:

If the RF Ground should prove to be of maginally high in impedance at
the Tx Frequency, then the transmitter, if it is not connected to
that RF Ground by anything but the coax, the transmitter will then be
part of the antenna system, as it will tend to float above the RF Ground
by the impedance at the Antenna Tuners Ground Stud. This can cause the
radio to do very strange things, and on occasion can cause RF Burns
when the operator transmits with the ground connected mic hanger
disc in his palm. Alot more common in, the old days of, fixed tuned
channelized antenna tuners. Autotuners just aren't as efficent at tuning
the antennas as the fixed tuner cannelized tuners.

Bruce in alaska
--
add a 2 before @