> It turns out that the shorter an antenna is
relative to a
> wavelength is, the higher the Q of the resonant antenna
system (antenna,
> transmission lines, coils, inductors and tuner) must
become to effectively
> radiate RF energy. And in achieving that higher Q using
coils and/or
> capacitors there is a good chance of increased losses due
to the higher AC
> currents and voltages involved.
The loss isn't that bad. See:
http://www.w8ji.com/mobile_antenna_fs_comparisons.htm
Ground loss dominates the system.
The real issue is all those extra turns hanging dead when
you go up in frequency. The same thing happens in antenna
tuners in roller inductors. You can get a series-resonance
in the coil and then voltages (and circulating currents) are
incredible. The antenna can also become very narrow banded
at the point were loss is highest. It really is a complex
interaction where the unused area of inductor behaves like a
pair of back-to-back L networks with extremely high values
of L and very low capacitance.
When an inductor is self-resonant or near self-resonance it
does not have anywhere near even current throughout. That's
what happens when all that extra coil isn't used. The same
thing happens in tank circuits and RF plate chokes.
73 Tom
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