[TowerTalk] Balanced Transmission Line

Richard (Rick) Karlquist richard at karlquist.com
Fri Feb 23 19:43:00 EST 2018


Nearly 20 years ago, I built a 1000 foot line 450 ohm line.
Here are some of the things I learned:

1.  The problems of ladder line go way beyond UV survival.  It is
quite a bit lossier than open wire line (OWL) when dry, but is a
disaster when wet.  It's impedance deviates considerably from the
claimed 450 ohms when dry, and deviates more when wet.

2.  If you are just running the OWL over the ground, as opposed
to up the air to the antenna, then you don't need line spacers.
What I do it support the line every 50 feet, and the line supports
enforce the spacing.  Between the supports, the wires stay sufficiently
parallel for ham radio work.

3.  I used stranded, aluminum, insulated (XHHW) wire, despite all
three of those characteristics supposedly being bad.  BTW, after
nearly 20 years of UV, the wire is doing just fine.  The measured
loss is close to the theoretical value.

4.  You mentioned transformers.  If you have a source or a design,
let us know.  What I did was build a 50 ohm unbalanced to 50 ohm
balanced balun in cascade with a 50 ohm balanced to 450 ohm
balanced transformer.  Rather than directly going from 50
ohm unbalanced to 450 ohm balanced.

5.  I've only used my line up to 10.1 MHz on the air, but just
for fun I optimized the design on the bench and got it to go
all the way from 1.8 to 54 MHz.  For maximum bandwidth, one trick
is to use 150 ohm line to wind the transformer, which is of
the Ruthroff type.

6.  I wouldn't go to Zo higher than 450 ohms.

73
Rick N6RK


On 2/23/2018 4:02 PM, Riki, K7NJ wrote:
> I'm currently in the planning stage of replacing a very long length of coax
> with open wire line with appropriate transformers at each end.   So far,
> I've only been able to find 450 ohm line, commonly called "ladder line" that



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