Antenna tuners 'like' antennas that are 'too long' better than
antennas that are 'too short'. That doesn't say anything about how
well that 'too long'/'too short' antenna will perform, just that the
average tuner will find it easier to deal with one that's 'too long'.
(Easier to 'cram' more capacitance into a tuner than inductance.) If
this antenna is a doublet, 'balanced', why would you need a
'groundplane'? And while I'd guess that it'll never be 'ideal', the
building is acting as a 'groundplane' anyway, sort of.
- 'Doc

(What am I not understanding about the situation?)

Antenna tuners 'like' antennas that are 'too long' better than
antennas that are 'too short'. That doesn't say anything about how
well that 'too long'/'too short' antenna will perform, just that the
average tuner will find it easier to deal with one that's 'too long'.
(Easier to 'cram' more capacitance into a tuner than inductance.) If
this antenna is a doublet, 'balanced', why would you need a
'groundplane'? And while I'd guess that it'll never be 'ideal', the
building is acting as a 'groundplane' anyway, sort of.
- 'Doc

(What am I not understanding about the situation?)


I don't think you are missing anything; your comments sound
reasonable to me. The building is the nearly new local firehouse HQ.
The Chief and staff have outlined very strict parameters for our antenna
location and setup. They fabricated the aluminum mast and will install
it on the side of the building per their own design. Even at that, they
gritted their teeth at the visual impact it has. No stand-off
supported open ladder line for us! We must work with this and I don't
see any feed alternative than coax. The only thing we 'may' have some
flexibility with is the length of the antenna. ( Sorry Cecil, I guess
I should have mentioned that up front ). We are limited to the length
of the side of the building, which I estimated would give us up to 40
feet of element from the top of the mast. However, in hindsignt, I
believe we could at that end point drop some additional length down off
the end for a longer antenna.... would probably give us better operation
on 75 & 80.


Ed

In article . 196,
"Ed_G" wrote:

we will be using an SGC-237 antenna coupler.

Comments?
Ed K7AAT

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 in alaska
add path after fast to reply

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

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
. 192.196:


Our ARES group plans on installing an Inverted V antenna on the
second story flat roof edge of a local building. The antenna mast is
13 feet tall above the roof edge. The Inverted V will run parallel the
edge of the roof and be approximately 35 - 40 feet per leg. Our
primary operations will be 80/75/40M with a desired ability on 60M.
The building custodian/owner will not tolerate open wire feedline with
its associated standoffs due to aesthetic considerations, so we must
feed this antenna with coax fastened to the mast. At the base of the
mast, on the roof, we will be using an SGC-237 antenna coupler.

The above setup is a given, with no room for compromise.

My questions for this group are as follows:

Would we be better feeding the above antenna feedpoint with twin
coax
runs, using the center conductors as a 'balanced' feedline, or would
we be better of using a single coax to the feedline? In either case,
the coax runs will not exceed 20 feet and we must accept the losses in
them. Email response from SGC seems to indicate we would be better

Ed,

I would consider the following:

Mount the ATU at an accessible place on the masting near the lowest end.
Bond the ATT's ground terminal to the mast.

If there is a lighting protection conductor, steel rain gutter, steel
roof in proximity of the base of the mast, bond the base of the mast to
them also using substantial conductors (16mm^2).

At the top of the mast, bond one side of the dipole to the mast.

Run an RG213 or better coax from the ATU to the top of the mast, bond the
shield at both ends to the mast. Connect the inner conductor at the top
to the other side of the dipole, and at the bottom to the output terminal
on the ATU. You must treat the ends of the coax to prevent water ingress.
LDF4-50 would be an even better choice because its closed cell bonded
foam dielectric is better protection against water ingress (it also has
lower loss and higher breakdown voltage). I would not use a foil shielded
coax.

Connect the DC / control wires and input coax to the base of the tuner,
but route them through a common mode choke. You may well be able to use
RG58C/U for the input feed line (depending on length). Wind several turns
of the coax and DC / control wires together through a large ferrite
toroid (#43 should be fine). Two or three of these chokes should probably
be adequate. You may also want one or two chokes where you enter the
equipment room.

Treat all connections to prevent corrosion, especially considering
dissimilar metals.

There is likely to be common mode current on the feedline / mast above
and below the tuner. The chokes reduce the extent of it to minimise the
contibution of the feedline to the radiation system / RFI and conversely
feed line noise pickup, and act to reduce RF "flowing into the shack".


off with a single feedline, but I am dubious about the SGC Tech Rep's
response since he/she does not seem concerned about feedline
radiation.

You can take measures as above to minimise the downsides of the lack of
system symmetry.

SGC have recommended attaching symmetric loads to their assymetric tuners
for a long time (they sell tuners, and didn't at the time have a balanced
tuner), and hams have proved it "works" whatever that means.


Also, what recomendations do you guys have for use of a balun?

See the discussion above about a common mode choke.

I
believe, at the least, we would need a 1:1 balun at the Input of the
SGC coupler so as to keep RF from getting back down the shield and
into the building. SGC response seems to indiate they don't think a
balun is necessary anywhere, which is another reason I am not
thrilled with their response.

See above.

Owen