[TowerTalk] TowerTalk Digest, Vol 154, Issue 1 Mounting 2 antennas on my mast

[Alfred Watson]

I have a Tennadyne T-11 on my Rohn 10 foot mast. Height of the antenna is just over 70 feet. Thinking about adding the Opti Beam rotary dipole 40/30 above it. Any suggestions/comments welcomed.  Tower is the 25 G Rohn, guyed at 35 feet and 70 feet. 
Al
W4ABW
Alabama
 
 
-----Original Message-----
From: towertalk-request <towertalk-request at contesting.com>
To: towertalk <towertalk at contesting.com>
Sent: Thu, Oct 1, 2015 5:06 am
Subject: TowerTalk Digest, Vol 154, Issue 1


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Today's Topics:

   1. Re: Interaction with the Optibeam 16-3
(StellarCAT)


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Message:
1
Date: Thu, 1 Oct 2015 09:24:04 -0400
From: "StellarCAT"
<rxdesign at ssvecnet.com>
To: <towertalk at contesting.com>
Subject: Re:
[TowerTalk] Interaction with the Optibeam 16-3
Message-ID:
<D384BB7B93E04612B9376C153AAE8883 at RXDesignDell>
Content-Type:
text/plain;	charset="UTF-8"

Steve,

Interesting.... my plans are for a
40M4LLDD mounted ~31? above the top antenna of a 2x6el stack on 15... when I
model something similar (I happen to, at the time, be looking at a moxon on 40)
I am seeing essentially no change in the SWR of the 15 and a reduction in the FB
of about 3 db (of course at a particular frequency ? from 33 db to 30 db). No
change in gain (actually a tiny increase as is not unusual) ... I had modeled a
20 stack (my plans are for 2x5el ? 20?s and the top one is 11? above the 40)
using the 20 stack and a full size 2 element 40 and this shows virtually no
interaction on 20 from the 40. I?d love to model the 40M4LLDD directly but
suspect it wouldn?t be correct using EZNEC6/NEC2. 

Bills question extended to
10 meters ? I?d suspect there?d be little interaction but it would be
interesting to hear about this (my main tower won?t have 10 on it) ... note as
others I?m sure have discovered ? if your SWR is effected by proximity of
antennas ? your FB is WILDLY effected! Generally the FB is the most sensitive.
Modeling guys for example ? the ARRL AB dimensions for ?safe lengths? ...
aren?t! They couple enough energy, I?ve tried a good variance of lengths, even a
good distance out from the tower, and they do effect the FB. Likewise my latest
modeling shows using only ~50? of philly nearest to the tower for the bottom 2
sets of guys and 70? for the top set does a great job with limiting interaction
to about 2 db worse case with no change in the gain or in the SWR. 

Gary,
K9RX
[still looking for R55 tower .... help?]


There is a big design
difference between a linear loaded M2 and a High-Q
coil loaded OptiBeam with
detuning stubs, however I think neither antenna
is resonant on 15m.  I do not
see any issued with the proposed layout.  I
am sure that DF2BO would be very
responsive if you asked OptiBeam this
question.
John KK9A
The M2 40M4LLDD is
close to resonant on 15 meters. I have one, and the SWR is about 1.6 across the
entire 15 meter band. I have even used it as a 2nd radio antenna on 15 meters.

I would be very cautious about putting it in close proximity to an Optibeam
16-3 or any other 15 meter antenna. 
73,
Steve,
N2IC


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