On 29 Feb 2008 00:51:16 GMT, "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
My SGC-237 is hard to mess up. Where ever you attach the wire to the
tuner is the beginning of the antenna. The coax attach will simply be
a matched line to the transceiver. I would be inclined to simply
attach the coax to the inverted V as you outlined and use it.

The antenna is in an environment that will not model well. The
radiation from the coax will have an effect on the aggregate
performance but nothing you can really measure.

Although I doubt anyone can explain just how it works, the SGC-237 and
the wire you have described will work fine.

Modern antenna tuners perform a lot like Magic in my estimation.

My own feeble experiments have led me to believe that it is worthwhile
to put an antenna analyzer on the configuration and make sure that the
array is NOT resonant on any frequency of interest. The tuner seems to
like that best.

Power supply: I have a very old telephone power supply tweaked down to
12 volts. I leave it on 24/7.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"