Rob,
I would switch in an inductor for a reflector and a capacitor for a director at
the CENTER of the element. Use a shorted stub for the reflector and an open
wire stub for the director.
The voltage at the ends is very high even in parasitic elements and you would
have the problem of RF getting into the switching wires. Not many relays will
survive that environment and I don't know anyone who has tried that.
I would try running 1/2 wave open wire line down to the ground and switch in
the lumped elements there. Then put lumped elements in at the antenna. Of
course you need split parasitic elements.
I have built 2 el 80 meter Yagis with a DE and Reflector using open wire
line(1/2 inch Al tubing) back to the center of the antenna so I could reach the
stub and adjust the shorting coil for F/B ratio. Then used a latching relay to
short out a portion of the line to go to the fone band. Of course a matching
network would have to be switched in going from CW to FONE.
But if you are working with wires, a spring loaded knife switch will work. But
you would have to go out to the tower to change directions.
I think I remember one guy who used retractable radio antennas from cars in a
junk yard.
And there is SteppIR if your VISA card can stand the hit.
I would be interested in other solutions myself.
Hardy N7RT/4
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Rob Katz
Sent: Sunday, October 16, 2016 11:09 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Voltage at ends of yogi parasitic elements?
I’m playing with some wire yagis, and I’d like to put relays at the ends of the
parasitic wires to switch the director to a reflector (and vice versa). If I’m
driving the antennas with a full 1.5 KW, what would be the maximum voltage that
I can expect at the ends of the PARASITIC elements? Even a rough estimate
would be useful, I just need to get a sense of what kind of a relay I would
need to use.
73,
Rob K4OV
--
Rob Katz, Senior Partner
919-219-5324
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