See attached reply to Al's original mail.
Subj: Fwd: [TowerTalk] Wire Yagis
Date: 97-02-25 13:39:04 EST
Subj: Re: [TowerTalk] Wire Yagis
Date: 97-02-25 13:14:21 EST
you are my kind of guy, bulding wire Yagi's. I have designed quite a few,
mainly for 80 Meters, I am currently using a 6 element wire yagi (switchable
NE/SW) with a common reflector. All wires are horizontal at about 100 feet.
Here are my general recommendations for your project (monoband wire beams):
Put the support rope (which will support your wires in the center) towards
the desired direction (i.e NE/SW) up as high as possible.
With a common reflector in the center of the array (5% longer than your
center TX frequency which you desire)
In front of the common reflector, 0.2 Lambda spacing, the driven element, cut
it by calculating 468/frequ and feed it with RG58 (I am using 1500W with my
80 M beam and RG58, it's much lighter than RG213), put a director , spacing
of 0.2 Lambda, 5% shorter than the driven element, in front of the driven
element. That's it. Same on the opposite side. That's it.
You might end up with an SWR of 1.5 to 1, but that comes with the design. If
you really want to monitor your progress, put up the driven element first, it
will be center frequency and a flat SWR, the moment you add the director or
the reflector you will see an increase in the SWR since your feedpoint
impedance changes to a lower value when you add the elements, but do not
worry. DO NOT USE A MATCHBOX !!
Now, with the two driven elements , put the two feedlines into an antenna
switch and drive either one line. You will see, when you switch to the
opposite direction, a difference of 12-15 dB compared to the signal in one
direction. It depends (on lower bands such as 80M ) also on the incoming
angle of radiation, but on the higher bands you will see these reults.
Good luck Al with the project.
Rolf, KE1Y (mainly on 3,795 +/-)
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