If a good ground grid is available at the base of the tower, I was thinking
of mounting a 40' boom, fixed near the top of the 125' tower. Each end of
the boom would have an 80M dipole hanging down from each end. This would
give approximately .15 wavelength spacing. Two feed lines would be run to
the middle of the tower and extended out on a 20' boom. Two 40M dipoles
would hang from the 20' boom. Each dipole has equal dimensions and feed
lines are run into a switchbox that would select in phase, or 90 degrees out
of phase by inserting an electrically correct 1/4 wave jumper. This is the
two element approach. It seems to me that the same could be done with 4
elements, but with more relays and another jumper. My biggest concern is
the tower impacting the end fire pattern. Thoughts?
-----Original Message-----
From: Jim Lux [mailto:jimlux@earthlink.net]
Sent: Wednesday, March 23, 2005 3:00 PM
To: Peter Grillo; 'StellarCAT'; towertalk@contesting.com
Subject: Re: [TowerTalk] Model done for 4SQ supported by center tower
At 01:38 AM 3/23/2005, Peter Grillo wrote:
>I've had similar thoughts. Whoever is willing to answer this question
might
>wish to suggest hanging vertical dipoles instead of requiring a ground
>planes under the vertical elements. Structurally, this would be a benefit.
>Same questions apply. Any takers?
Sure, you don't have to have a ground plane for the "other side" of the
dipole, but ground effects due to loss in the near field will still be
evident. How would you run feedlines? horizontally (catenary) from the
tower? Up the inside of the element to the half way point (decoupling is a
challenge, but maybe the currents on the feedline as it goes away from the
bottom could be compensated some other way).
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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