[TowerTalk] Re: Coil loss

[Bill Fuqua]

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