[TowerTalk] Stacked tri-banders vs. Single mono-banders

[John Brosnahan]

>
>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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