Date: Fri, 3 Jun 2016 11:15:22 -0400
From: "StellarCAT" <rxdesign@ssvecnet.com>
To: "tower" <towertalk@contesting.com>
Subject: [TowerTalk] Exploring another option re interaction 40/15 on
same tower
Ok ... so the plan is to have 6/6 on 15M at 90/45 and I?m worried about (the
unknown) interaction from a 4 el 40 mounted 34? above the top 15.
One option I have is to simply rotate the 40M 90 degrees and mount it that way.
I already have the 80/75 dipole turned that way so the rotor has to have an
?offset? reading capability (Green Heron) ... so why not just ?extend? that to
40 as well. I have a rugged mount that will allow it to be mounted on the 1.5?
leg of the Rohn 45 with an arm that goes out to a second leg for added
reinforcement ...
I don?t know if there is an adverse effect between 80 and 40 ? the 80 dipole is
~76? long with hi-Q coils at the center and 26? T bars out 2/3rd of the way to
the end...
There might still be an issue of the boom of the 40, 42? long, interacting with
the top 15 but it would be considerably less than the full antenna I?d guess...
but only a guess.
does anyone have any issues with this? I know the wind load is going to be
changed to put it lightly ... but with 6 antennas on this tower ? all
substantial in size that might actually be a good thing making it less
susceptible to the desire to ?point it in to the wind? (for as we all know we
can?t always do that).
thoughts?
Gary
K9RX
## Does the entire tower rotate ? If so, just mount the 40m yagi 90 degs
to the pair of 15m yagis below it... problem solved. The 42 ft boom of the
40m yagi will not screw
up the top 15m yagi..nor the lower 15m yagi. If your 80m rotary dipole is
mounted so its inline with the 40m boom, the 80m will not affect the upper
/lower 15M.
The 26 FT long T bars on the 80m will now be 90 deg from the 15M
eles.... which is good. Those 26 ft T bars will resonate around 18
mhz....which might affect the top 15M array,
but that’s a moot point, since the T bars will be 90 degs to the 15M eles.
( ditto with the 40M eles...also 90 degs to the 15M eles).
## optibeam used 8 x stubs to detune their version of the 4 el 40M. That
plus their coils are not very far out from the boom. F12 N type 40M eles
use LL rods, but again,
they are not far out from the boom, only 7 ft 9 inch. f12 didnt use any
decoupling stubs..... however it resonates around 24 mhz... which will screw up
a 12m ant.... but solves the 40 + 15m interaction issue. ( without having to
offset the booms by 90 deg).
## If ur sleeve idea works...and shifts the 3rd harmonic resonance up in freq
a bunch.....( like way up..as in 24+ mhz)..... then u wont have to rotate the
40 /15m booms by 90 deg.
## If u have a top rotor for the 40 + 80....and side mount rotors for the pair
of 15s... then you might have to rotate the 80/40...but only when operating
on 15m. If ur sleeve ide works good, then u wont have to do that, and
everything can rotate independent of each other.
Jim VE7RF
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