[TowerTalk] Phasing verticals and stubs
clive.whelan at btinternet.com
Wed Apr 5 12:05:32 EDT 2006
<When all three elements are used, usually one is driven with 100%
current, and the other two are driven at the same phase with about 50%
current each. The beam directions are off the top or the bottom of the
triangle (so they are moved around 60deg compared with the two-element
case). The gain is higher using all three elements, but beam switching
is much less simple so you may be practically restricted to only three
Another arrangement is due to W1CF, and is also described in the ON4UN book.
This also employs an equilateral triangle, but with 110 degree sides, and
provides six directions of 60 degrees each firing off the points or the
sides, as Ian described. In this case for simplicity equal powers are used,
and a phasing line is added. This can be used with multiband verticals on a
number of bands, but compromises are inevitable, and I use an auto-tuner at
the base to cope with the complex impedances presented. Most significantly
of course, the base of the triangle is varying, in a three band arrangement
from 55 degrees up to 220 degrees. I find that at the "half size" point,
directionality is still good and seems still to be at the 60 degree points.
However at the wider "double size", it seems to fire bidirectionally in two
selectable directions. In my case three HF9Vs are used on a 40ft triangle.
The phasing line in theory needs to be different for each frequency, but
EZNEC suggests that a single chosen length is within 0.5dB of the maximum
gain on all ( contest) bands. This arrangement works outstandingly well for
me on 40m, very well on 80m, and tolerably on 20m. On 15 & 10m, the
performance is probably just equal to a single vertical, although
surprisingly there still appears to be directionality. It also works on the
WARC bands, with clear directionality, but undetermined performance-30m may
be close to 40m I suspect. In practice on 40m, this arrangement will come
close to a "shorty forty" at about 60ft. Oh did I mention, you need a good
ground system; mine is a virtual bog! If you can get a tower and a decent
yagi airborne, do it. I can't so the above does a job for me.
More information about the TowerTalk