SGC coupler to Dipole feedling question
 

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

SGC coupler to Dipole feedling question
 

"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

SGC coupler to Dipole feedling question
 

In article . 196,
"Ed_G" wrote:

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 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.

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

Comments?


Ed K7AAT

hi Ed

you might try using a plastic mast (pvc or fiberglass) with enought
strength to survive the load and weather thats hollow and try running
laddar line inside

you can use some solid plastic pipe some ham places sell it or
even a short piece ofmetal mast if you can cut a small slot in
the plastic such that it's integraity is good or u can run the
laddar line down the outside of the plastic pipe pprobably easist
and paint it all black w/rf ok paint very hard to see the feed line
then


way back when i spoke to somone that was 'smart' at sgc and they said
using a short piece of laddar line to feed the dipole (as they way i
happened to do mine almost exactly as you described) they said it was
less than ideal but not bad as long as the laddar line was i believe
less than 10??ft long they said the output definately shouldn't
have any balun as far as the coax feeding the tuner?? most
seemed to agree it wasn't needed but i thru one in anyway both on
the roof and in my shack


my set up thou slightly different than yours unscientifically seems to
work very well, i don't have nasty stuff on my coax run to the tuner
my swr even w/a very short dipole is nearly almost always max at 1.2
worst case the tuner tunes in seconds and i've enjoyed some pretty
good fun the total length of my dipole is maybe less than 40ft

is my set up ideal? or good as a beam? i'd guess not but i had co
op board roof constraints as you sorta have so it's best effort
and i've had a blast with it from 160 to 6m


i got a bunch of my ideas for it's actual design and final construction
from my fooling aournd , here in this group , sgc personal I think i
spoke to the original owner once, there manuals and googling


goodluck Ed

SGC coupler to Dipole feedling question
 

In the past, I normally have always used a balanced tuner on my
balanced antenna systems..... this one under discussion, being one of
those SGC antenna couplers, is NOT balanced..... It did not occur to me
that the currents through the twin coax feedlines to the balanced
antenna would not be equal. So, to make sure I am understanding you
correctly, this un-symmetrical current could also occur in open ladder-
line?

Obviously the weakness of my antenna knowledge has been exposed. My
thanks to Roy, AND to Owen.


Ed
Just curious, how did this project turn out?
John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.

SGC coupler to Dipole feedling question
 

In the past, I normally have always used a balanced tuner on my
balanced antenna systems..... this one under discussion, being one of
those SGC antenna couplers, is NOT balanced..... It did not occur to
me
that the currents through the twin coax feedlines to the balanced
antenna would not be equal. So, to make sure I am understanding you
correctly, this un-symmetrical current could also occur in open
ladder-
line?

Obviously the weakness of my antenna knowledge has been exposed. My
thanks to Roy, AND to Owen.


Ed
Just curious, how did this project turn out?
John Ferrell W8CCW
Beware of the dopeler effect (pronounced dope-ler).
That's where bad ideas seem good if they come at you
fast enough.


Appreciate the inquiry, but due to my pending move in early May (
local ) We have not yet completed this project. Rest assured, I
remember the information presented in the discussion on this thread and
intend to proceed..... probably later in May when my move is completed
and I am available to assist the other members of the team that will be
installing the aformentioned antenna. TNX

73 de Ed K7AAT