Date: Sun, 02 Jun 2013 11:26:12 -0400
From: Everett Jackson <wz8p@wz8p.com>
To: towertalk@contesting.com
Subject: [TowerTalk] 15 Meter and 40 Meter on the same tower?
I have a 135 ft rotating tower.
I am wanting to put a 5 element 15 meter beam on a 36 ft boom
and a 3 element 40 meter beam on a 46 ftboom on the same tower.
How much space is need between them? Or is this just not a good idea to
start with?
73,
Everett – WZ8P
## My F-12 340N ... 3 el – 40m yagi does not resonate on 15m. However it
will screw up a 12m yagi.
So it all depends on the design of the 40m yagi. F-12 claims you can put
those 40m N type eles within
3 feet of a 20-10m yagi... with no interaction. I think the N eles resonate
just above or below the 12m band.
## You also have to be careful when 2 yagis are at right angles to each other.
years ago, folks would try and use a KLM KT34XA with a KLM 3 el yagi.... it
doesn’t work. 40 + 15m
would interact badly..with both pointed in the same direction. If one yagi
rotated 90 deg, the 40 + 15m interaction
is now zero, but a new problem arises. The 32 foot long boom of the KT-34XA
will screw up 20M band real bad !
## So the Fix was not to use the 3 el klm 40m yagi on the 32 foot boom,.....
but to instead use the klm 4 el 40m yagi on the
42 foot boom. Then when at right angles, no interaction on any band.
## You get those kinds of problems when using stuff like tic ring rotors.
with a rotating tower, it is not an issue.
N6BT told me you can get another kind of effect too..and that’s when you
mount a physically larger 40m yagi above
a smaller 15m or other band yagi. It’s a shadowing effect.
## In your case, it’s a tough call. You might want to put the 40m yagi as
high as you can......and then put the 15m yagi down lower..
a lot lower. Like maybe a 135 + 80 type of combo. With 55 feet of
separation, it may work.
If we assume the 40m yagi resonates on 15m.... can’t this interaction be
modeled on eznec, etc ??? Put an MFJ on the 40m yagi
or get somebody who has the SAME 40m yagi as you do, to do the test..and sweep
the entire HF spectrum... and find out exactly
where it resonates. IF it doesn’t resonate on 15m, its gotta resonate
some where !! That also pertains to any ant. If they don’t
resonate on their 3rd harmonic, they gotta resonate some where.
## Come to think of it, most ants may well resonate on their 5th + 7th
harmonic as well..but don’t quote me on that.
My old quarter wave sloper on 80m would resonate on 6M ..with a flat swr...go
figure.
Later... Jim VE7RF
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