>
>You *may* be right, but in my book, a TH-7 is not a modern
>tribander. The antennas you mention have trapless driven elements
>which go a long way towards improving efficiency.
>
>I have used both, from similar locations at similar heights,
>and yes it is a subjective judgement, but there is no substitute
>for a good monoband stack. Even small yagis, if properly set-up,
>would be much preferred than the " 1/2 dB here, 1/2 dB there
>it's not such a big deal" solution you are selling.
While I agree in theory that tribanders are compromises and that
I would much prefer to have stacks of optimized monobanders I went
ahead and installed a 4-stack of TH-7s this summer (with the help of
K9AN--tnx, Steve). This was done as an expedient since I already
owned four unused TH-7s that were purchased a number of years ago
and I had an old TH-6 and a TH-2 that were given to me and were
"married" to make the fifth TH-7.
The 4-stack was installed on a rotating 175 ft Rohn 55 tower at
40/80/120/160 ft--also on the tower were two KLM 4L 40M Yagis
at 90 and 172 ft, and the fifth TH-7 was at 45 ft on a Tic ring on a
separate tower. I was concerned about interaction of the 4-stack
with the 4L 40s but decided that although this was a potential problem
I would leave the 40s on the tower for future all-band efforts and they
would better represent a "typical" installation that is compromised
by other antennas within the array.
This fall I decided to see how the station plays on 20M with tribanders.
This was designed as an "experiment" to see just how many and
how big 20M monobanders would need to be in order to be really
competitive on 20M. Historical experience from K0RF and other
stations in the region seemed to indicate that it is hardest to be
competitive from Colorado on 20M relative to the other "higher" bands,
40 through 10 meters. And since W0UA and N2IC have won plaques
from W0UN on 40, 15, and 10 M it was time to see just what was
possible on 20M. At least we could obtain some sort of benchmark to
determine what I would have to do with big monobanders in the future.
The results in the CQWW CW contest with W0UA operating were quite
encouraging. Here are the top high-claimed scores from Jimmy, K4ZAM
(and a major thank you for all of his efforts to collect scores is warranted).
K8DX 792,442 1700 4922 36 125
W0UN (W0UA) HP 775,008 1686 4784 38 124
K9BG 25 454,000 1022 2910 38 118
N7BZ (@NK7U) HP 441,700 1082 33 107
KO6N (AE0M@N6RO)HP 29 407,772 1158 2892 38 103
A very strong second place finish in the high claimed scores is very
encouraging. This score not only represents a good showing in this
particular contest, it also represents a new 0-district record. But even
more encouraging is that it represents a score that breaks the existing
records in 3, 4, 5, 6, 7, and 9-land as well. Leaving only 1, 2, an 8-land
as targets!
I think that the limit to the score was the single TH-7 at 45 ft. For a
significant part of the contest 20M was open to both Europe and Asia
and we were forced to spray in both directions and the second direction
just had a tribander at 45 ft--not very competitive. It would have been
much better to have something like a 2-stack of TH-7s or a pair
of 204s for the second direction. I think the race with K8DX would
have been MUCH closer with almost any competive ARRAY for the
second option.
So I have learned not to sell stacked tribanders short. While I still
believe that monobanders are superior, of course, in the case of big
arrays the array factor seems to dominate over the individual antennas
used in the array. I think I would prefer a 2-stack of big tribanders over
a single monobander in most cases (subject to installation heights
of course--a single big monobander at 200 ft can do some
phenomenal things at times!).
So stacked tribanders ARE competitive and also reduce the total
amount of clutter (and windload) on the tower. They also reduce
the issues of interaction that stacks of interlaced monobanders
would raise when trying to do 4-stacks of monobanders for three
separate bands on the same tower.
John W0UN
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