Pull up an inverted L and try it, there is no other way to find out how it
will work for sure. Even if you have poor connections between sections, and
the beams are isolated from the tower, there are still coax and control
lines that go up the tower, those would act as a vertical conductor even if
the tower itself doesn't. and trying to model or even guess how those wires
will interact with anything else is pretty well hopeless. In a complex
environment like that there is no better way than 'Plug it in and try it!'.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: Jack White [mailto:m5pro@hotmail.com]
Sent: Thursday, December 27, 2012 15:50
To: Towertalk
Subject: [TowerTalk] 80M Ideas
Hi
I've been reading the ON4UN book and antenna articles online on and off for
a couple of years now but I thought I'd share my situation with some more
experienced Guys on here to see if I can perhaps find some new information
and ideas.
I have a modest HF/6 station that covers 40-6. I have a painted 3 section
60ft Versatower (suspect v. poor electrical connection between sections)
with an Optibeam OB1-4030, Optibeam OB9-5 and 5L 6M Yagi all mounted on a
15ft stub mast and fed into an Array Solutions Ratpak. (Antenna pic on QRZ)
The 6M Yagi has grounded elements but the Optibeam elements are insulated
from the boom and tower. The station is working nicely now so I feel it's
time to add an 80M DX TX antenna. I am interested in 3.5MHz CW only, so
bandwidth/phone etc not an issue.
In the past I've tried an 80M coax fed inverted vee with the apex at 60ft -
as expected dynamite out to a couple of thousand miles but no good for DX.
I've ruled out the possibility of shunt feeding the tower because of the
Optibeams and the poor connection between sections. So currently I'm left
with two ideas:
MFJ-1792 or Butternut HF2V mounted 50ft from the tower (landscaped gardens
prevent mounting anywhere else)
Inverted L hanging off the tower with approx 60ft vertical section.
What I guess really matters is the tower's resonant frequency, looking at
the details above, would anybody like to guess? Because the Optibeams are
insulated from the tower do they still effect the tower's resonant
frequency? If it is resonant close to 80M I guess the RF fed into a vert
50ft away would see it as a parasitic element?
In the worst case scenario, if the tower messed with a vertical I could
always lower it before operating on 80M but it's not ideal.
Apologies for any stupid questions and Merry Christmas to you all!
Jack G8DX
Sent from my iPhone
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