[Elecraft] Good Low Horizontal Loops - questions

[k6se@juno.com]

Lyle, KK7P wrote:

"Sorry, the statement "*must*" is not true.  You can feed any antenna
with any feedline if you are willing to accept the consequences of
operation at frequencies where there are impedance mismatches (the
feedline|antenna interface and the feedline|transmitter interface)."
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If you feed an antenna for use on all bands, those bands it is not
resonant on will have current on the coax feedline shield and the coax
will also radiate -- an undesireable trait.  The feedline will not
radiate if you use a balanced feeder.

The only correct way that I can think of to feed an antenna as an
all-band antenna using a coax feedline is to place the "antenna" tuner at
the feedpoint of the antenna.  A good tuner there can match virtually any
feedpoint impedance to 50 ohms at any frequency, resulting in a 1:1 SWR
on the 50-ohm feedline.
==========

"Sometimes you can use this to your advantage (e.g., a "matching
section")."
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Using a matching section (i.e., the 75-ohm quarter wavelength of coax I
mentioned before to match 50-ohms to a 100-ohm feedpoint at the antenna's
resonant frequency) makes the system a single-band system, not only
because of the matching section, but because it's a coax-fed system.

Matching sections can also be made out of open-wire line for use with
balanced feeders, but that makes it a single-band system also.
==========
 
"Open-wire high-impedance balanced feedline tends to have lower losses
than coaxial cables because the dielectric is air, and at high SWR
(between the tuner and the antenna) dielectric losses become very
important, often exceeding the resistive (e.g., copper) losses if you are
using a tuner."
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I don't disagree with that statement, except that the tuner does not have
anything to do with the dielectric or copper losses on the feedline.
==========

"One reason Wayne's suggestion works so well (toss one end of a wire into
a tree, attach the other end to the KAT2 output on your K2) is that there
is, in effect, no feedline. See the ARRL Antenna Book."
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I agree with that.  Jusr remember to use a counterpoise of at least one
wire with such a system.

73, de Earl, K6SE