Date: Thu, 23 Nov 2017 12:17:33 -0500
From: "Gene Smar" <ersmar@verizon.net>
To: <towertalk@contesting.com>
Subject: [TowerTalk] Relay for sloper element
< I want to be able to switch a piece of #14 house wire onto the far end
<of a sloper wire I have for 75 M phone so I can operate lower in the band.
I'm thinking of adding a relay in a weather-resistant box at the sloper's
end insulator and continue with the extension wire beyond that.
My question to this august group: What relay (and supplier) would you
recommend for the job?
In the alternative, can you point me to a good source of info on
designing traps for said application? The trap would not require any DC for
switching but might take more "cypherin' " to get working.
Many thanks and Happy Thanksgiving to all y'all.
73 de
Gene Smar AD3F
## Ok, this is a quarter wave sloper. A trap wont work, since you just want
to be able
to move the resonant freq down a bit. The far end is sky high voltage, esp
with 1.5 kw,
so dont add wire at the extreme end.
## Install a spst relay or a DPST relay... with contacts in parallel. The
DPST relay, with contacts
in parallel, will provide for doubling the RF current capacity and also
provides for redundant contacts.
Use a 12 vdc relay coil, then feed it with 13.8 vdc from the shack.
## A small coil, like with wound with a total of 4 foot of wire would shift
the resonant freq down by
250 khz. All the relay does is, shorts the coil out. A 3 inch diam coil
has a 12 inch circumference,
so 4 turns would suffice. Or use a smaller diam coil and a more turns.
Install the coil at the feedpoint,
next to the tower. A 40 A sealed spst automotive type relay would work, as
will a lot of other relays.
The peak V at the 50 ohm feedpoint is aprx 388 volts...assuming 1.5 kw into
50 ohms.
## another method is to use bigger gauge wire to begin with. 10 gauge wire
is a LOT more broad banded
vs 14 gauge... when using qtr wave slopers. Im talking about the main
sloper, not the coil. 14 gauge
will work just fine for the small coil.
## either a separate control cable for the 13.8 vdc.... or a bias T will
work. I have used both schemes in the
past. If u just want to shift the res point from say 3850.... down to say
3600, the above coil + relay setup
will work just fine. The default will be the lower freq, with coil
de-energized. If u use a NC relay, then its
the other way around.
Jim VE7RF
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