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

good stuff by Meindert snipped

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

Hi Norm, I'm still learning to use EZNEC http://www.eznec.com/ modelling
software, but I will ask a friend who works with it often to run some
typical backstay offerings and see how it portrays various configurations.

Best,
Jack Painter
Virginia Beach, Va

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

"Jack Painter" wrote in message
news:luPtc.221$Y21.126@lakeread02...
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!

Precisely! :-)

My wires and dipole are of course half wave devices and at
desired frequencies do not even require a tuner at all.

Aha, there's the catch..

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.

It all depends on proper tuning. Your 4:1 balun might not be enough on short
wires. Try a 9:1 balun. But anyway, it is always betten not to use a low
impedant cable like coax between a tuner and an antenna.
This might explain your wonder about the ability of vessels to get good
performance. At a vessel, the cable run from tuner to antenna is mostly (I
hope :-) ) short and made of GTO15 or similar stuff. If you, on the other
hand, use coax to the antenna, even with a 4:1 balun which is not
transforming high enough, you have a problem tuning it properly.

If you have the chance, try a balun (1:1) directly after the tuner, better
yet, use a symmetrical tuner, and feed a dipole with open line (two wires,
spaced 3" apart). This will give you:
A) better tuneability and B) better surpression of man-made noise. To
prevent the feeders from radiating, you could add a common-mode choke in the
feeder (sometimes called a current-balun).

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?

Only if you feed the 1/2 in the low impedance point, which is halfway in the
middel. Since this is impractical on a boat, feed it at the endpoint. But at
the endpoint of a 1/2 wave, the impedance is very high so you need the least
capacitance you can get at the antenna feedpoint. So GT15 is ok, but keep it
1" away from any grounded or other conductive area (like strapping the GTO15
to the uninsulated lower part of the backstay with tie-raps... BAD
PRACTICE).

Meindert
PE1GRV

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


good stuff by Meindert snipped

:-)

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.

Precisely

My opinion is that the lead, whatever it is, between the ATU and the
*real* antenna, becomes part of the antenna.

Indeed, it will radiate as much as the antenna does. Therefore it is best to
place the ATU immediately at the feed point of the backstay. The best
practical place would be directly below deck, underneath the backstay. Every
effort to keep the GTO15 as short as possible is best.

Meindert

"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

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.

Well as I mentioned previously, Icom's printed literature on
antenna/transciever installation recommends grounding the transmitter to the
same ground ("boat ground") as the tuner using foil. Of course the Icom
tech that I contacted about this said not to ground the radio so everyone is
confused about this..................

"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.

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

I know that one has to be careful that a suffucuent DC ground is
provided in addition to the RF ground. Otherwise high currents
can be drawn though the RF ground with bad results. I personally
have never heard of no grounding the radio to the RF ground. If
you look at the manual for most any HF rig you will see that it
requires an earth ground to a stud on the back of the rig. Seems
to me that connecting this to the RF counterpoise makes sense.

Doug, k3qt
s/v Callista

"Gordon Wedman" wrote in message
news:mYIuc.10643$ig5.6123@edtnps89...
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.

Well as I mentioned previously, Icom's printed literature on
antenna/transciever installation recommends grounding the transmitter to
the
same ground ("boat ground") as the tuner using foil. Of course the Icom
tech that I contacted about this said not to ground the radio so everyone
is
confused about this..................

"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.

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