There is literally no benefit to do the switching at the ends. But there
are a lot of reliability issues so why take the hard road when there is no
performance increment - and at the same time the headaches with that
solution are going to be ongoing. The HV switch is going to have mass and
is going to be an ice accumulation point if you have weather. I would bet
you good money that if you go with an end-switched solution in a couple of
years you are going to be in the "what was I thinking?" camp...
My antennas were run in KW level RTTY and I never had a relay issue with a
the phasing control stuff done in the center - the voltage there is low and
the currents high but that's a much easier fix than trying to put a HV
switch out on the ends of an antenna.
Good luck!
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Kelly Taylor
Sent: Tuesday, October 18, 2016 1:24 AM
To: john@kk9a.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Voltage at ends of yogi parasitic elements?
I should add that it doesn’t change needing a robust switching mechanism to
handle the voltage, but at least resolves the issue of conductors to switch
a relay being in the vicinity of the antenna.
73, kelly, ve4xt
On Oct 17, 2016, at 12:10 PM, Kelly Taylor <ve4xt@mymts.net> wrote:
John’s old idea seems like the perfect application of something in QST a
while back: a pneumatic relay.
A puff of air up a non-conducting piece of tubing would trigger the
switch: I can’t recall if it was latching or not.
73, kelly, ve4xt
On Oct 17, 2016, at 11:44 AM, john@kk9a.com wrote:
That is a good question. Years ago I thought of building an 80m vertical
with a relay on top to make it a 160m inverted L at my P40A home but I
did
not know if even a vacuum relay would hold up and I knew that there would
be RF issues with the control wires running down the vertical. I had
never
seen it done and did not want something likely to fail. If you are just
changing band segments most manufactures are using switchable loading
coils at the feed point.
GL
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Voltage at ends of yogi parasitic elements?
From: Rob Katz <rob.katz@thelegacycenter.com>
Date: Sun, 16 Oct 2016 23:09:11 -0400
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
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