[TCML] New 3.5" Coil - A kick in the right direction please!
tcml87 at abelian.org
Mon Sep 22 09:26:07 MDT 2008
Just a minor correction here...
> If you "really" want the secondary wire length to be 1/4
> wavelength (such as antenna theory, radio circuits, etc.)
> then realize you can't use a top load.
Actually the effect of winding the wire into a solenoid will
*increase* the resonant frequency above that of the straight
wire, by a factor of about 1.5 to 1.7 for a typical secondary.
Therefore it is possible to choose a topload capacitance which
will pull the resulting bare coil resonance back down to that
of the original straight wire resonance. Nothing special or
useful happens if you do this, though.
For example, if Grant wound his 340 metres of wire into a
solenoid of h/d ratio 3.5, the resonant frequency of the
unloaded coil would be about 1.6 times 220kHz ~= 350kHz.
A large topload, with a capacitance about 2.5 times that of
the coil's self-capacitance would be needed to pull the
resonance down to 220kHz.
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