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Re: [TowerTalk] remote control of antenna switch via "wired" UHF

Subject: Re: [TowerTalk] remote control of antenna switch via "wired" UHF
From: Jim Lux <>
Date: Sun, 01 Jan 2012 09:05:08 -0800
List-post: <">>
On 1/1/12 7:18 AM, Pete Smith wrote:
> I am planning to build, in the next couple of days, the couplers needed
> to test this idea.  To revisit it, I have qn inexpensive RF-controlled
> 8-way band switch, and several people suggested that I should couple the
> RF from the "remote" to my feedline, and pick it off the other end, to
> eliminate path losses over the ~300 foot range.
> This seems plausible to me, but as usual I'm having trouble figuring out
> the specifics.  Say I take a piece of RG-59, remove the jacket and the
> shield braid, and then couple the output from the remote to the center
> conductor moni-match style.
   Should I lay the coupling wire parallel to
> the center conductor, or should I wind it around the insulated center
> conductor?  What sort of total length for the coupling wire would give
> best results at ~315 MHz?  Any difference in the design of the coupler
> on the receiving end?

I would think you're looking for capacitive coupling, more than anything 
else (and to be honest, you could probably couple to the OUTSIDE of the 
coax.. the earth serves as the "other side" of your decidedly non 
constant impedance transmission line.

So figure, you want a couple pF.. (at 300  MHz a pF is 500 ohms..)

If you put the shield over your coupling probe, you'll probably couple 
more power to the shield than to the center conductor (closer, larger 
capacitance, etc.)

> I assume I should pull the braid back over the "coupler" section - is
> that right?  If I have common mode chokes (#31 toroids) on both ends of
> the feedline, will it be better to have the couplers between the chokes,
> or doesn't it matter, since the UHF RF will presumably be going by
> differential mode?

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