Ok, first thing, NONE of the Lumped Constant Binary Switch Tuners like
SGC's Knockoff of the SEA Design, will tune ANYWHERE within a few
percent of the Natural Halfwave Point of the antenna. So you must
design
the Antenna, so as to move that Halfwave Point to a section of the
HF Spectrum that you NEVER plan on using. Second thing, none of the
SGC
Employees around today, were around when this Tuner and it's Operating
software was designed, and most don't have much experience with actual
operational considerations.
Thirdly, After a lot of experimentation with the SEA1612b Series
Tuners,
from which the SGC's were plagiarized, when using them to drive a
dipole, there are two schools of thought. One school says that you
should add a 1:1 Balun on the output of the tuner between the RF
Ground
Stud, and RF Output Connection to make your Balanced Feed. Second
school
says to take the Feedline Coax, Dc Power Lines, and Tuning Feedback
Wire, and wind them, in a Bifilar fashion on an appropriate Torriod
to decouple the Tuner from Radio Feed and connect the dipole to the
RF Ground Stud, and the RF Output Connection.
I have used both Systems on Maritime Mobile Limited Coast Stations,
around Alaska, and find that they both work about Equally Poor. It
should be noted here, however that Alaska is notorious for not having
any kind of decent RF Grounding Soil, so usually this type of Antenna
System works much better than an type of Longwire antenna that needs a
good RF Ground, to work against. Where a GOOD RF Ground is available,
(Salt Water) the Longwire Antenna outperforms the Tuner Driven Dipole,
ever time, but without that GOOD RF Ground, the Tuner Driven Dipole
works better than just about anything else, especially over a wide
range
of Frequency Bands available, in both the Maritime and Amateur Radio
HF
spectrums.

Bruce in alaska


Bruce,

Thanks for the response to my query. I have a couple comments to
these. One, we already own a new SGC-237 coupler, so that is what we
will use. Two, thanks for the info on the SGC personnel.... that
might explain why some of their responses to my emails didn't seem to
make sense... especially their comments about NOT needing any balun.
Three, and more direct to my initial questions, it appears we will be
using coax between the coupler output and the antenna feedpoint.... up
to 20 feet of low loss... we'll just eat the loss. But more
importantly, I had intended, and will proceed along the lines of your
comments on baluns, by installing a 1:1 balun at the input to the
tuner. This will, at least, keep the RF out of the building and our
station location.

thanks.

Ed

In article . 196,
"Ed_G" wrote:


Bruce,

Thanks for the response to my query. I have a couple comments to
these. One, we already own a new SGC-237 coupler, so that is what we
will use. Two, thanks for the info on the SGC personnel.... that
might explain why some of their responses to my emails didn't seem to
make sense... especially their comments about NOT needing any balun.
Three, and more direct to my initial questions, it appears we will be
using coax between the coupler output and the antenna feedpoint.... up
to 20 feet of low loss... we'll just eat the loss. But more
importantly, I had intended, and will proceed along the lines of your
comments on baluns, by installing a 1:1 balun at the input to the
tuner. This will, at least, keep the RF out of the building and our
station location.

thanks.

Ed


Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each end
and sealed against water intrusion. Even if taped to the aluminum mast.
This would provide a much better situation than a single coax feed.
Also if you are stuck with a single coax, then make SURE, that the
shield side of the coax is connected to the Ground Stud of the tuner.

--
Bruce in alaska
add path after fast to reply

Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each end
and sealed against water intrusion. Even if taped to the aluminum
mast.
This would provide a much better situation than a single coax feed.
Also if you are stuck with a single coax, then make SURE, that the
shield side of the coax is connected to the Ground Stud of the tuner.



Well! That was part of my original question in this thread! I had
intended to do just that, but some here seemed to steer me toward a
single coax, including SGC personnel. I do NOT think we have any
decent ground at all available anywhere near the roof location where
this antenna mast will be located, so I was unsure if the twin coax
feed would be OK without grounding the shields. Left floating, I
don't know what effect, if any, we will have for incidental radiation.
One thing for sure, it won't be any worse than using a single coax with
no balun at the feedpoint.


Ed

In article . 196,
"Ed_G" wrote:


Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each end
and sealed against water intrusion. Even if taped to the aluminum
mast.
This would provide a much better situation than a single coax feed.
Also if you are stuck with a single coax, then make SURE, that the
shield side of the coax is connected to the Ground Stud of the tuner.



Well! That was part of my original question in this thread! I had
intended to do just that, but some here seemed to steer me toward a
single coax, including SGC personnel. I do NOT think we have any
decent ground at all available anywhere near the roof location where
this antenna mast will be located, so I was unsure if the twin coax
feed would be OK without grounding the shields. Left floating, I
don't know what effect, if any, we will have for incidental radiation.
One thing for sure, it won't be any worse than using a single coax with
no balun at the feedpoint.


Ed

"Left Floating" so that there is less Capacitance to RF Ground, and more
distance between the vertical parallel Feedlines. It would even help
if you can use twin Coax Runs, to put them on opposite sides of the
Aluminum Mast, which would give you more separation with the same
Coupling Capacitance to the Mast. Capacitive coupling to RF Ground,
is the Killer here, and you MUST reduce that, as much as possible,
if your system is going to have any chance at reasonable operation.

--
Bruce in alaska
add path after fast to reply

"Left Floating" so that there is less Capacitance to RF Ground, and
more distance between the vertical parallel Feedlines. It would even
help if you can use twin Coax Runs, to put them on opposite sides of
the Aluminum Mast, which would give you more separation with the same
Coupling Capacitance to the Mast. Capacitive coupling to RF Ground,
is the Killer here, and you MUST reduce that, as much as possible,
if your system is going to have any chance at reasonable operation.



Please read my response and question just posted to Owen. With both
shields tied together, but not grounded, nor connected to the antenna
either, I do not understand how common mode current is an issue on the
shields.

We could use the mast as a physical separation as you suggested, (
the mast is not grounded, either, but again, what is the point, if the
two coax shields were "as one" anyway?


Ed
I

Ed_G wrote:

Please read my response and question just posted to Owen. With both
shields tied together, but not grounded, nor connected to the antenna
either, I do not understand how common mode current is an issue on the
shields.

We could use the mast as a physical separation as you suggested, (
the mast is not grounded, either, but again, what is the point, if the
two coax shields were "as one" anyway?

I hope my recent postings have helped answer your question.

Roy Lewallen, W7EL

In article . 196,
"Ed_G" wrote:

"Left Floating" so that there is less Capacitance to RF Ground, and
more distance between the vertical parallel Feedlines. It would even
help if you can use twin Coax Runs, to put them on opposite sides of
the Aluminum Mast, which would give you more separation with the same
Coupling Capacitance to the Mast. Capacitive coupling to RF Ground,
is the Killer here, and you MUST reduce that, as much as possible,
if your system is going to have any chance at reasonable operation.



Please read my response and question just posted to Owen. With both
shields tied together, but not grounded, nor connected to the antenna
either, I do not understand how common mode current is an issue on the
shields.

We could use the mast as a physical separation as you suggested, (
the mast is not grounded, either, but again, what is the point, if the
two coax shields were "as one" anyway?


Ed
I

Most of the discussion here is more esoteric, than practical. You have
an imposed Antenna Requirement, that gives you little wiggle room in
what you can do. I have given you the ideas, that are proven in the
Real World, for installations with similar requirements. As I stated
in my first post, these type systems, ALL preform equally BAD, when
compared to the Antenna Systems, that these type tuners were DESIGNED
to feed. They are intended to feed a Marconi Vertical, with a very
Low Impedance RF Ground. That is where they work BEST. Everything else
will be a poorer situation. How poor, will depend on a BIG pile of
variables, most of which are esoteric in significance, and will
not make a significant difference in actual Practical Performance of the
Station. Again as I stated in my last post, Capitative Coupling to
RF Ground is the BIG Killer, the second largest problem is selecting
antenna length, so as the Natural Impedance of the antenna is NOT
anywhere near a frequency that you need to operate on. All the rest,
is Picking Nits, and can be discussed at infinitum, without changing
the actual performance in any significant way. One of the posters
suggested building an "counterpoise", (God, I hate that Term) RF Ground
from Aluminum Alarm Tape, on the roof, and then feeding what would be
essentially a end feed wire antenna. That would be preferable, IF you
could get the Biggies to go along, but that was NOT, part of the
original Problem. In the real WORLD, your Comm's are going to depend
more on, if the Band is Open, for your Distance, and Frequency, to
the destination, than the Antenna design, and if the Band is NOT open,
you aren't going to talk, as Ground Wave Comm's are not usually a
significant part of HF Communications.

Just a note, for historical purposes. There was a highly modified
SEA1612B Tuner that was designed to feed a Balanced Antenna. It was
fabricated out of Two, (2) Tuner Boards, using a Common CPU/Sensor
System, that determined the configuration of the Switched Elements
on one side of the Antenna, and then locked the same configuration
on the Second board for the other side. This scheme was developed
by Don Hollingsworth Sr. at G&L Marine Radio, in Seattle, Washington,
and was deployed in one or two installations of Maritime Mobile Limited
Coast Stations. I never did hear just how well they worked.

--
Bruce in alaska
add path after fast to reply

Bruce in alaska wrote in news:fast-25B5D6.09195501032008
@netnews.worldnet.att.net:

....
Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each end
and sealed against water intrusion.

What does this do, what does it achieve?

Owen

Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each
end and sealed against water intrusion.

What does this do, what does it achieve?

Owen



My expertise is weak in this area, but just guessing.... using twin
coax in the above configuration, if the shields were grounded, would
allow the feedling between the antenna coupler and the feedpoint to be
'balanced' and yet the shields would not radiate as they would with a
single coax run.

Perhaps others, here, will either expand on this, or correct my
misconception.

Ed K7AAT

"Ed_G" wrote in
.91:


Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each
end and sealed against water intrusion.

What does this do, what does it achieve?

Owen



My expertise is weak in this area, but just guessing.... using
twin
coax in the above configuration, if the shields were grounded, would

But that is not what was said. I read it to say "with the shield left
open on each end".

allow the feedling between the antenna coupler and the feedpoint to be
'balanced' and yet the shields would not radiate as they would with a
single coax run.

Bunk. The only reason the shields would not radiate would be if they
carried equal but opposite currents. That is most unlikely in this case.

Let us just consider a simple example. Assumption is that skin effect on
the coax is fully effective, a reasonable assumption at HF.

Make a quarter wave vertical of a piece of RG213 supported on sky hooks.
Make no connection to the shield at either end, and connect the feed line
between a ground plane / counterpoise / whatever and the centre conductor
of the vertical piece of coax.

What current flows on the outside surface of the vertical coax?

The current on the outside surface of the vertical coax adjacent to the
bottom end of the isolated shield is the same as the current flowing on
the inner conductor adjacent to the same end of the shield.

Does the outer conductor 'shield' the vertical so that it will not
radiate?

No, the outside surface of the shield is the radiatior, it just has a
quarter wave o/c stub in series from the feedline to the radiating
element.



Perhaps others, here, will either expand on this, or correct my
misconception.


Owen