Part three of many
Art wrote:
"---thus to follow the intent of Maxwell`s law we must first extend the
antenna to a full wave form."
False. All we need is resonance to eliminate reactance which otherwise
would limit current in the antenna . First resonance in the thin
straight 1/2-wave dipole ia about 5% less than a physical 1/2
wavelength. A full wavelength straight antenna has characteristics
completely different from its first-resonance cousin.
A small diameter coil radiates perpendicularly to its axis. As a
radiator its effect is related to the coil`s length not the length of
wire on the form. Wire length is related to resistance to r-f current
and therefore to loss in an antenna containing coils. That is the source
of skepticism of the Unwin antenna. Resistance-loaded antennas have
proven useful in situations demanding great frequency bandwidth so Art
may have something of value after all.
My ARRL Antenna Book (20th ed.) says on page 16-13:
"The general approach has been to use a coil nade from very heavy wire
(#14 or larger), with length-to-diameter ratios as high as 21. British
experimenters have reported good results with 8-foot overall lengths on
the 1.8 and 3.5 MHz bands."
Bill Orr wrote on page 78 of "All About Vertical Antennas":
"In general, a half-wavelength of no,14 Formvar-coated wire is spirally
wrapped on the form, with turn spacing approximately eqial to the wire
diameter. This amount of wire will approximate a quarter-wave resonance.
Orr`s book was first printed in 1986. Unwin has a problem with novelty.
Best regards, Richard harrison, KB5WZI
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