I have been using a 3 element parasitic vertical beam on 160 for at least 20
years. K9CT, NR5M, AA1K*, VE3EJ and most recently W5ZN have the same array.
It has instant switching in 4 directions.
With 4 parasitic cut directors around the center driven element tower - it
is pretty easy to get over 5 dB of forward gain (over 40 KHz wide) and over
30 dB of front to back (over a narrow bandwidth). Easy driven element match
with an L network at the base. Each parasitic has 3 modes. Director,
Reflector or float. Going from directional to Omni is easy as well.
*AA1K has an additional director toward Europe. So he has 4 elements!
As was pointed out - the magic in any vertical antenna is all about the
radials. Each parasitic wire (4) and the center driven element tower has 120
radials that are 130 feet long (unless they cross the junction bus). I have
67,000 feet of radials under my 160 array.
I use a 120 ft 24 inch face solid leg tower as the driven element. The tower
sections are welded together to decrease any joint loss. The parasitic T
wires are #12 Copperweld.
The last three editions of the Low Band DXing book describe this antenna in
the Yagi chapter.
73
Tim K3LR
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of W7RH
Sent: Tuesday, January 30, 2018 11:39 PM
To: Topband
Subject: Re: Topband: Adding a parasitic reflector to a vertical
I've played with parasitic elements in antenna arrays for almost three
decades and the current antenna system I have used parasitic elements
both director and reflectors.
With very careful tuning performance that of a all driven array can be
achieved. Tree is correct they due tend to be somewhat limited in in
bandwidth with relation to F/B ratio. Gain remains fairly constant.
The tuning procedure that Tree suggested is absolutely correct. You
detune all unused elements and adjust the center frequency of the
parasitic for best F/B one element at a time. Parasitic elements I might
add are no different than driven and must have extensive ground system
to be effective. No exceptions. You know you have right by F/B ratio.
You can go one step further and measure the actual antenna currents
which I have done. In my system the parasitic elements achieve 80-85% of
the theoretical current at the base.
de Bob W7RH
--
W7RH DM35OS
It has become appallingly obvious that our technology has exceeded our
humanity.
Albert Einstein
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