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Old November 29th 07, 08:03 PM posted to rec.radio.amateur.antenna
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Posts: 274
Default Loading Coils; was : Vincent antenna

Cecil Moore wrote:
Gene Fuller wrote:
Second, your analysis is utter rot! Are you suggesting that if the
coil can be made resonant at some frequency, and then you cut it in
half, that it still behaves the same?


No, it behaves approximately like half of the original
coil tending to have approximately the same Z0 and VF as
the original coil. The phase shift through the coil will
tend to be approximately 1/2 of the original phase shift -
not exact because of end effects.

Let's say we have a 1/4WL helical antenna with an obvious
phase shift of 90 degrees. If we cut that helical in half,
it is likely to have a phase shift of approximately 45
degrees, nowhere near the 4.5 degrees that W8JI has
"measured".

If we add a stinger to the above half-coil, we will have
a base-loaded antenna. The phase shift will be relatively
close to 45 degrees at the same frequency. The stinger
contributes another few degrees. The impedance discontinuity
between the coil and stinger contributes the rest of the
90 degrees of electrical length.


"Utter rot" is a pretty good description of this. Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.
73,
Tom Donaly, KA6RUH
 
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