[Antennas] Balanced line optimum conductor spacing?

[DGB]

I believe I remember reading a clear explanation of that in
an ARRL Antenna Handbook a while back.

73 Dwight W9YQ

----- Original Message -----
From: "Tom Scott" <tomrscott@sterlink.net>
To: "'Antennas Reflector List'" <antennas@mailman.qth.net>
Sent: Friday, January 04, 2002 17:58 PM
Subject: [Antennas] Balanced line optimum conductor spacing?


> All the discussion of window line (which I've always
preferred) and ladder
> line, got me to wondering if anyone has seen any
definitive tests or
> analysis of the effects of the spacing between the two
balanced conductors?
>
> For a given frequency there should be a tradeoff between
wider spacing that
> yields lower loss and higher impedance versus poorer
balancing of the
> complementary fields surrounding the two conductors. I
seem to remember
> reading somewhere that 0.1% of the wavelength was a good
compromise, but I'm
> not certain. That would suggest that for the 10m band you
should use 10mm
> wire spacing (~0.4"), and for the 160m band you should use
160mm wire
> spacing (~6.3"). It seems that most home-built ladder line
I've seen is
> built with something on the order of five to six inches
spacing, while
> window line is around 1 inch or a little less, so this
calculation seems
> like it's in the ballpark. Since we hams have a nasty
habit of wanting to
> operate on multiple bands, I'm just curious how much
balance you lose with
> real wide conductors when operating from a higher
frequency band, and how
> much extra loss you get when you operate narrow spaced
lines on a lower
> frequency band.
>
> Probably not too significant, but just something that got
me wondering.
>
> As I recall, the NEC2 models don't yield much useful
information about
> balanced lines.
>
> Maybe one of the transmission line calculators could give
the results of
> this analysis. Of course there are other factors, like
conductor quality and
> diameter, dielectric quality, etc.
>
> - Tom Scott, Field Applications Engineering
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