[TowerTalk] 4 Square phase line length question

[Jim Lux]

----- Original Message -----
From: "Dan Levin" <dan at andlev.com>
To: <towertalk at contesting.com>
Sent: Saturday, May 08, 2004 3:13 PM
Subject: [TowerTalk] 4 Square phase line length question


> We are building a 4 square, and using Force 12 relay boxes to tune the
> elements for phone and CW.  These boxes put a coil in series with the feed
> point of the antenna to electrically lengthen it for CW, and then short
out
> the coil using a relay for phone.
>
>
>
> Question: Do we need to take into account the length of the wire in the
coil
> (on CW) when we calculate the length of the RG-11 phasing lines from the
> hybrid coupler to each element?  To put it differently, are the coils part
> of the antenna, in which case we make the phasing lines the right length
and
> ignore the coils, or are the coils part of the feed line, in which case
they
> effect the length for phasing purposes?
>
>
The series coil is there to cancel the capacitive reactance of the too short
antenna. (and, because the element's not "that much" shorter, the resistive
part, (mostly radiation and ground resistance) is about the same, so if you
take out the extra C, the match is fairly good).

However, in a 4 square (or any driven phased array), the feed point
impedances aren't even remotely close to what a single element would be, so
the value of switching in a coil is dubious.

Here's the interesting thing..I assume you're using some scheme where you
use 1/4 wavelength lines for current forcing, right? so the element current
will be what it should be, regardless of the element impedance.  The
mismatch at the feed eventually winds up back at the hybrid/phasing network,
where you can take it out by changing the L or C of the phasing network (or,
just ignore it, and take it out at the array feed point).




>
> Thanks!
>
>
>
>                                     ***dan, K6IF
>
>
>
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