[TowerTalk] Re: Coil loss

[Bill Fuqua <wlfuqu00@uky.edu>]

You are probably right about the ground loss. In a balanced system the 
dominate loss will not be ground loss but
you can't escape higher  Q  with short antennas.
    I'd prefer a vertical antenna with an attached tuner if possible. But 
it is more complex
and more costly.

73
Bill wa4lav


At 02:17 PM 6/2/2004 -0400, Tom Rauch wrote:
> >          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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