On 10/15/2017 7:24 PM, Paul Christensen wrote:
What caught my attention was this statement in the article's second
paragraph: "The solution is to add an inductor at a multiple of a
half-wavelength-long feed line, and its *effect will be the same* as a coil
at the dipole feed point."
I normally try to restrain myself from bashing QST technical articles,
because they are such easy prey :-)
Besides the loss problem you mentioned, a more fundamental problem is
that a half wavelength line is only a half wavelength at one
frequency, presumably the center of the band. As you tune away from
that frequency, the 1/2 wave line is no longer just an attenuator
as you report, but it acts to reduce the bandwidth of the system.
The more multiples of a 1/2 wave, the more reduction.
The other issue is that he cut the dipole for the high end of the
band and then tuned it down with an inductor. What I have been doing
for a long time is to instead locate a capacitor at the feedpoint
with the normally closed contacts of a relay across it. The
dipole length is adjusted for CW, and the relay is energized to go
to phone. An Omron MJN series relay from Mouser and a single 220 pF
1 kV mica capacitor are used. The switchable capacitor is in series
with the center conductor of the coax at the "line" end of the common
mode choke. The choke is just a big toroid with coax wound around
it. I mount all this in a plastic box. It works fine for inverted vees
where there is a support at the center. Even if the support is just
a 3 inch thin wall irrigation pipe held up by ropes.
Rick N6RK
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