I've seen various posts where 2 pieces of coax was used to run between the
balanced output of a tuner and through walls and windows to get to a
balanced feed line. In general, this approach totally un-necessary and I've
found that it usually doesn't work very well either. Should one find it
necessary to run a balanced feed through a window, as long as the frame is
not metal there is no problem. Just run the line through and close the
window. However, in the case of a metal frame, I suggest using a couple of
1/2" thick strips of adhesive backed weather strip, one on the bottom of the
window sash and one on the frame. Run the feedline through and close the
window. Of course it won't close all the way so some concern and method of
security must be devised. A stick propped from the top of the sash to the
top of the frame prevents the window from being opened in a double hung
window arrangement. Same true where one has awing type windows, just put a
couple of strips of weather strip between the pane and the frame.
For those that choose to use the twin coax method, by connecting the shields
together at the antenna feed point and again at the tuner end produces a
"shorted turn" and yes, one will have trouble loading the arrangement. It
is strongly suggested that one connect shields at one end only if you choose
to use this method, ideally at the tuner end. Be reminded that the loss in
coax goes up drastically with higher SWR values even at HF frequencies.
This is the main reason for using "open wire" feed systems in a severe
mis-match situation. The dielectric loss is very low, even with high SWR
values. As to power handling abilities, since dielectric loss is low on
open wire feed systems, the practical power limit is simply the IR loss of
the conductors. With coax operating with high SWR values, it must be
de-rated in terms of power handling to account for heating due to dielectric
loss. The heating is being generated by RF which is not
radiated.........except as heat.
I'm not sure about the true intrinsic value of the TITANEX feedline. Looks
expensive and not likely to work very well.
73
Bob K4TAX
----- Original Message -----
From: "George Osier" <gosier@twcny.rr.com>
To: "Ten Tec Group" <TenTec@contesting.com>
Sent: Monday, October 14, 2002 5:20 PM
Subject: [TenTec] TWINCOM feedline ?????????????
> Hello All !!!!!
>
> While looking thru antenna makers listed on the net I went to TITANEX
> ........ Incredible antennas !!!!!
>
> But what caught my eye was TWINCOM feedline that looks like a combination
of
> normal cord used for appliances and coax .................. 250 ohm but
> similar in respects to ladder line ....... seems like it would be a good
way
> to get closer to the performance of ladder line ????????????
>
> Anyone ever use this stuff and what did you think ????????????
>
>
> 73s
>
> George Osier , N2JNZ / QRP
>
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