I used 2" spacing on my acrylic plastic spacers, with 20 gauge solid copper
wire, so maybe 200 Ohms impedance? But with it I could load all bands with
my tuner from 80M-10M.
73,
Steve
N6SJ
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Rob Atkinson
Sent: Sunday, December 31, 2023 3:23 AM
To: towertalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Open-wire transmission line
I think we should back up and get more information from the fellow asking
for help. It's understandable to assume the question pertains to a pair of
wires but open wire line is a term encompassing different designs. For
example, the line could be an unbalanced line with a coaxial geometry with a
large center conductor and four or more smaller diameter conductors spaced
around it equidistant from the center and each other. Or, it could be a
balanced line with an even
number of conductors greater than two. In that case, two pairs of
different diameter may or may not work (I'm not sure offhand). So, to the
ham asking for help, please tell us what design of open wire line you are
attempting to assemble. If in fact it is two wire balanced line, there's no
good reason I can think of for one wire diameter to be different from the
other, and I'd like to know why you are trying this other than wire
availability. As N6RK said, different diameters will lead to different
resistances, different currents, and line loss via radiation. Therefore,
formulas are irrelevant because you
shouldn't do it. BTW from my experience, AWG 16 copper stranded
works fine for US ham power levels. For a reasonable impedance for
multiband use (600 ohms), going wider diameter will mean spacing insulator
length of 5 or more inches. 600 ohms line Z is sort of the target if you
are going to use a center fed half wave dipole as a load across multiple
bands with half wave length on the lowest frequency because 600 ohms is
roughly in the middle of the load Z extremes.
73
Rob
K5UJ
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