Wayne,
I have done a ton of modeling and think the direction you are heading (with
the multi-monoband on a single boom sort of Force-12 design) is the best way
to go.
Multiple monobanders on a single mast works but it's not without
compromises. I have at my QTH a set of OWA 4-element beams on a single mast
spaced about 7' apart. The stack with this minimal spacing has tons of
interactions that are easily revealed in models. In my estimate, the gain
takes a 1-2 dB haircut and the F/B pulls back around 5 dB. And the
response of the beam really picks up for signals coming down vertically to
the array - which means more band noise.
While monobanders are the ideal antenna, when you get them next to something
else, the interactions start to penalize. And you don't need too much of
that to push your shiny new stack down to the level of what a good
single-antenna gives. You don't have any of these performance issues with a
well designed forward staggared design like the 31 or similar. There are
compromises to the design vs. a stand-alone monobander - but I think these
are slight in the overall scheme.
What may be as important for a crank-up would be the lack of a tall mast
sticking out, and as such you eliminate torque at the top of the tower. You
can put more antenna on the single boom mounted close to the top of the
tower than you can spread over 15' of mast sticking out of the tower.
So you may ask, if the forward staggared stuff looks so good as I suggest,
why did I put up the monobanders? The answer is that I wanted to run M2 or
So2r in contest work. And here, the physical spacing along the vertical
mast with the monobanders gives me a high natural band to band isolation and
separate feedpoints per band that I cannot get (at least not to the same
extent) with a multi-band, single boom design. But I gather that is not a
factor in your choice. Hence the recommendation for the single boom
antenna.
As a practical comparison, a buddy of mine has an old force-12 at 90' - his
setup is consistently on par with my 3x monobanders and we are able to work
the same dx at about the same reliability level. I forget what he has but
it's 2 elements per band, 10/15/20/40. This kind of story has a zillion
variables in it but it serves as a sanity check. To the first
approximation, the two "arrays" work in the same ballpark.
If it were me, I would stick with the modern era designs. Optibeams, the
Force-12 stuff, etc. Stay away from stuff with traps and stuff that no one
can explain like the M2/KLM 34/36. But there are a lot of guys running
Hygain 6/7/11 stuff out there that have great signals - it's not that these
antennas don't work, but rather I believe the newer designs to be better
engineered and less mechanically complex.
One thing to consider - there is a ton of DX on the WARC bands. You could
argue that soon 12m will be a dead band and that's going to be true. But 17
will be good for a long time and is a great band. I would consider
seriously an antenna that is designed with performance on this band. Even
if it ended up costing me 12/10. Not sure if theres a variant on the market
(other than an LPDA) that would do that but my point is just to consider the
WARC bands if you are serious about DX.
Good luck!
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: K8RI
Sent: Thursday, April 18, 2013 10:10 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Please Help Me Decide on a Tribander or Monobanders
His question is whether to choose the tribander or monobanders I've seen
very little that has addressed the original question.
73
Roger (K8RI)
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