Fw: Re: Fw: Fw: Re: [Antennas] 450 Ohm Ladder Line

[Cletus W Whitaker]

de WB2CPN South Central Pennsylvania  2002.12.15

Being an innocent young idiot new to electronic communication
theory a long time ago I fell for a "QST" April Fool joke.
I had fabricated a few 20-Meter folded dipoles from a very
heavy duty flexible 200-Ohm parallel wire transmission line,
and they all were extremely narrow band and impractical.
The QST article said "Underground Antennas" would work, so
I buried one about 6 feet deep in a long trench.  First, it
eliminated most of the noise I heard in my receiver, and
it also made working a station a few blocks away the same as
working rare DX.  Really though, the main effect of the wires
being surrounded with dirt was that it lowered the resonant
frequency of the dipole significantly.  I don't think the
losses were increased because all the 500 watts went down
into the ditch someplace.  I've used a lot of "ladder line"
since then, but almost all in a Zepp or resonant mode.
Two major factors affecting loss; the dielectric loss in
the separator and nearby material, and the ohmic resistance
of the conductors.  Being wet doesn't matter much, and being
covered with salt or grime only increases loss if the ohmic
shunt resistance is increased.  The effect is more noticeable
at the point where there is a voltage maximum on the line.
The 600-Ohm open wire transmission line used with simple
HF transmitter facilities used either a Delta Matched dipole,
or a three-wire folded dipole.  The delta matched antennas
were easier to adjust at the transmitter end.
               73  Clete