[TowerTalk] RF & DC coupling/decoupling

[T A RUSSELL]

Dale -

You neglected to mention the frequency (frequencies?) that will be
present
on the feedline.

It is fairly easy to simply put an inductor from the center wire of the
coax
to the DC supply and DC load with sufficient L to isolate the RF from DC.
An absolute minimum value for XL would be 500 ohms, preferably higher,
say 5000 ohms.  You will probably want a good RF by-pass capacitor on 
the DC side of each coil.

Another approach is to use a parallel resonant circuit (coil and
capacitor)
between the center wire of the coax and the DC source and load, again
with an RF bypass capacitor to ground on the DC side.  This reduces 
the size of the coil needed but will only work on a single frequency.

de  Tom  N4KG
............................
On Fri, 19 Dec 1997 01:03:37 -0600 "Dale L. Martin" <kg5u@hal-pc.org>
writes:
>I have checked my resources here in the shack (ARRL Handbook and ARRL
>Antenna Handbook and beaucoup issues of old QST's) and find nothing to 
>help
>me in my quest to the following question:
>
>What components are needed to couple/decouple a DC control voltage 
>(13.8v)
>on a coaxial cable which will also carry 500 W RF?
>
>Does anyone have a working system  such as this?  I've seen them
>referenced/described in the past, but now that I need it, I can't find 
>any
>info on it.
>
>What component values of C1, L1, C2 and L2 work?  Are there any other
>additional components used?  If you have such a system, are you been
>satisfied with the performance?
>
>I have a marine vertical antenna and automatic antenna tuner at the 
>end of a
>600 foot run of 7/8" hard-line.  Rather than install a power supply in 
>a
>nearby rooftop equipment room, I would like to see if 
>coupling/decoupling
>the DC would work in it's place.
>
>Thanks in advance for any information.
>
>(apologies if this is not Tower related, but they won't let me put up 
>a
>tower on the roof directly above the station).
>
>Dale Martin, KG5U
>kg5u@hal-pc.org
>http://www.hal-pc.org/~kg5u
>
>
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