Why couldn't you use a dual voltage output power supply?
https://www.amazon.com/Dr-meter-Single-Output-Switchable-Alligator-included/dp/B0749CD2V3/ref=sr_1_3?ie=UTF8&qid=1512072780&sr=8-3&keywords=dual+voltage+output+power+supply%3F
Tom, N2SR
From: Gene Smar <ersmar@verizon.net>
To: n8de@thepoint.net; towertalk@contesting.com
Sent: Tuesday, November 28, 2017 3:45 AM
Subject: Re: [TowerTalk] Relay for sloper element
Don:
Thanks for the note. I believe ( I haven't actually diagrammed this
out on paper) that using the +/- voltage on coax would short out the shack's
DC supply when I connected the + to ground. The negative terminal of the
shack DC supply is connected to all chassis metal and coax shields, so
connecting the supply's positive output to the coax shield would place a
dead short on the DC supply's output terminals. I'd have to use a separate
DC supply (wall wart) and ensure that the two output terminals are never
connected to ground. I don't like the idea of a separate, noise-producing
PS so I'm not favoring that solution. Using a separate DC cable, with two
isolated DC lines plus shield, would provide the isolation I'd need to
invert the polarity of the relays' DC supply.
73 de
Gene Smar AD3F
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
n8de@thepoint.net
Sent: Monday, November 27, 2017 2:40 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Relay for sloper element
Why not use the coax to carry switching voltage?
0v for condition 1
+12v for condition 2
-12v for condition 3
and with some ingenuity (designed by ME in 1970's) 12v AC for condition 4
which allows FOUR bands with one wire antenna.
73
Don
N8DE
Quoting Gene Smar <ersmar@verizon.net>:
> Jim:
>
> Thanks for your suggestion. If I use a DPDT center-off switch on
> the DC supply in the shack and steering diodes in the relay box at the
> tower top, I can use two relays to short out part or all of the
> loading coil at the feedpoint. That way I'd end up with 60M (coil
> shorted), 75 M (partial
> coil) and 80 M (full coil) on the same wire.
>
> I now recall seeing this feedpoint loading technique for a
> half-sloper wire (the more correct term) like mine in QST a number of
> years ago. I hadn't thought of using a relay to make the wire
multi-banded.
>
> Using a bias-T in this configuration would short the positive DC
> bus to ground in one switch position, so I guess that's out. Carrying
> the DC to the tower top in a two-conductor-plus-shield cable would
> isolate the positive and negative leads from ground at the tower top,
> as the relay coils would not be grounded in any configuration.
>
> Regarding the paralleling of the DPST relay contacts, I'll
> probably do that. In this configuration (loading coil at the feed)
> the feed is the high-current point and having parallel contacts will
> minimize the contact resistance through which this current must flow.
> Also, as you pointed out, it provides a bit of redundancy.
>
>
> 73 de
> Gene Smar AD3F
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> Jim Thomson
> Sent: Monday, November 27, 2017 8:28 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Relay for sloper element
>
> 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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