Useful information Tom.
K8CC and I have been talking about an in-line tribander with 2 meters in
front of 6 meters and 432 in front of 2 meters. No intercalation. I *think*
you can intercalate the elements but the design becomes much more difficult.
For a small beam with 2 elements {Moxxon] on 6 and maybe 6 el on 2 and 10-11
el on 432 that is still only about 15 feet long. No problem for a fixed
location but the smaller size for a rover antenna would be nice - if it can
be done. The number of feedlines depend on the individual situation. For
someone with some talent and a K3 Elecraft, the K3 can do all your switching
seamlessly. For an FT100 or IC706 you are better with separate feedlines or
if running less than 200 watts some kind of diplexer for 2 and 432.
The Cushcraft is clearly NOT the way to go. I think - at a price - the
Ariane Arrays tribander would have done the job but they are gone now. Quad
driven elements work well but you still have a 3 dimension problem for all
those elements. Linear yagis are better mechanically IF you can get them to
work right. Wayne's gain figures for a 3 el multiband quad seem to be in the
right ballpark, Maybe K8CC can homebrew something linear that is
reproducable and cheap.
Dave will likely have some comments on what I've said. It's relatively easy
to talk about it but the devil's in the details of how to do it in real
life.
73 Gene W3ZZ
-----Original Message-----
From: Tom Carney [mailto:tomc@carneysugai.com]
Sent: Saturday, March 06, 2010 6:19 PM
To: Eugene Zimmerman; VHFcontesting@contesting.com
Subject: Re: [VHFcontesting] Getting beginners interested in VHF Contesting
Interesting discussion. I am primarily a rover and face somewhat a similar
requirement to simplify the antenna situation. For me, it's more the desire
to minimize the time to put up and take down the antennas than the cost.
First comment, since the 706 (and FT-100) have two antenna connectors, I'm
not convinced it worth the trouble to go for a single feedline. If you do,
you end up with some form of duplexer at the radio end of the coax. Or at
the least, a coax switch. I have a similar problem in feeding a 2M and 432M
antenna from the single antenna connector of the radio and tried a switch at
first but would frequently forget to switch the antenna. A duplexer is
similar in cost to the extra feedline up to 50/60 feet. More if you use
RX-8X for 6M.
I've tried modeling several different antennas just to get 2M and 432 on a
single boom without much success. The presence of the 2M elements seems to
distort the 432 pattern. At least that what EZ-NEC predicts.
For example, I recently modeled a dual band yagi that appears to be a
Cushcraft A270-10S. This antenna has five elements on each band. The
elements for one band are mounted above the boom, the other band below.
Cushcraft quotes 10bdi gain for each band, but EZ-NEC predicted only about
8 dbi on 432. Remove the 2M elements from the model and the gain jumps over
2db.
Perhaps some form of quad might be a solution, haven't tried that. The N6NB
pack uses a three element multiband quad for 2, 222, and 432 and Wayne
quotes a gain of 7-8 DB over a dipole.
73,
Tom K6EU
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