Re: SGC coupler to Dipole feedling question


"Ed_G" <Huckleberry_REMOVE_@xxxxxxxxxxxxx> wrote in message news:Xns9A52AB752D939Huckleberrybigvalley@xxxxxxxxxxxxxxxxxx

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

If the SGC-237 coupler is on the roof and properly grounded, try it the way the SGC rep suggested. Any feedline radiation should occur from the antenna side of the coupler and might help with getting a bit more signal out. Go with the simplest solution first and run a single coax to the coupler from the transceiver. Maybe it will work just fine.

If there are problems with RF on the coax outer, add some ferrite beads over the coax to form an RF choke.

Look at more complex solutions when you have actually identified a problem rather than worrying in advance over something that probably won't happen.

Mike G0ULI

.

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