----- Original Message -----
From: "Frank Mayer" <email@example.com>
To: "Jan Erik Holm" <firstname.lastname@example.org>
Cc: "'towertalk'" <email@example.com>
Sent: Thursday, November 18, 2004 6:29 AM
Subject: Re: [TowerTalk] 80m 4Square Comtek box
I use a variable phasing network for my 2 4BTV verticals that I use on 40
and 20 meters. The phasing unit consists of a roller inductor in series
with one antenna and a 500pf variable in series with the other antenna. The
outputs of those 2 components are joined and feed an antenna tuner connected
to the rig. I have a DPDT toggle switch so I can switch the 2 components to
the opposite antenna to change directions. The antennas are 17' apart and
have a cardioid pattern on both bands with at least 20 to 30 db front to
back. I just wish there was some way I could measure the forward gain. It
is within 1 s- unit of my 2 element yagi on 40 to VK and ZL.
This isn't a bad approach, and works well with 2 elements. There might be a
fair amount of reactive power circulating through the feedlines, but,
feedline loss is reasonably low, so it's not all that bad. One can do a
similar thing with a pair of screwdrivers or compact loop antennas (tune one
a bit high, and the other a bit low, and the ATU takes care of transforming
the parallel combination to something the transmitter likes to see).
1 S-unit is 6dB, and in the phased array business, 6 dB is a huge variation
in gain, especially for a 2 element array. Consider that the 2 element yagi
only probably has about 4-5 dBi gain in the first place. The F/B is mostly a
matter of nulling, which your setup will do quite nicely.
It's really tough to make work with 4 elements. Greg Ordy has a great web
page talking about his "adventures" with various strategies.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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