On 24 Jun 2006 17:45:43 -0700, wrote:

The BuxComm Antenna Company sells what it calls an All Band Coax-fed
Dipole.

http://www.commparts.com/catalog/pro...ffad91005875fb


It consists of 135 ft. of wire, a balun at the center feed point, and
the RG 8X coax transmission line. I don't claim to know a whole lot
about antennas, but this configuration is contrary to everything that I
have read about feeding mutiband antennas. When I wrote to the company
with a question about this, I received a response from K4ABT, Buck
Rogers himself. He attached to his note a section from the ARRL Antenna
Book, which seems to indicate that coax should not be used with this
type of antenna if one wants to use it as a multibander. I have a lot
of respect for Buck, based on his years of Elmering a lot of us through
his articles. But this one has me stumped. Any input will be
appreciated.

It all goes to the meaning of "works".

You will need to make your own mind up about what losses are
acceptable.

You should expect that the feedpoint impedance of that antenna at
resonance around 7MHz is about 4200 ohms.

The loss in 25m (~75') of RG8X will be about 8.3dB, or about 15% of
your transmitter power reaches the balun.

If you used a quarter wave of RG8X, the worst case line loss is around
0.7dB (or about 15%) per meter near the transmitter, that indicates
60W/m dissipation in that region at the 400W continuous power rating.
I doubt that RG8X is suited to this antenna on 7MHz at 400W
continuous, but with the lower average power level of voice SSB, it
should not be an issue.

The balun power rating and losses are another issue with this load
impedance, but in the absence of detail on the balun design, I will
say not more than more information needed!

There was an article in QST some time back visiting the issues with
multiband operation of a dipole with coax feed. The article was
centred around a 66' dipole, but the lessons apply to your prospective
purchase. I wrote an article at http://www.vk1od.net/LOLL/index.htm
reviewing the QST article, there are links to the original article and
some other relevant articles at the bottom of mine.

Owen

PS: Nothing here is to suggest you wont get QSOs.
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