[TowerTalk] Homebrew loading coils

[Mark .]

Hello All,
I have been making some loading coils for shortened HF verticals, and I 
could use some advice from those more experienced. I am making multi-tapped 
coil assemblies with alligator-clip jumpers for achieving resonance on 
short, end-loaded wires> They are similar to the 'Texas Bugcatcher' mobile 
HF antenna style, except with capacity hats all the way at the top of the 
radiator.

I am using enameled or insulated wire (different versions) wrapped around 
PVC pipe coil forms, and covered over with electrical tape. One problem I am 
running into is that the number of turns required to resonate the antenna 
lower and lower in frequency is not a linear relationship.
For example, it takes significantly more than double the turns to go from 
7.2 MHz to 3.9 Mhz. It is more like triple. Is this normal, or am I getting 
inter-turn capacitance in my coil that is reducing its effectiveness?
I plan to try switching to bare wire with more spacing between turns, and to 
use spacers in 4 places around the coil form so that the wire only touches 
the plastic in 4 places per turn.

Any suggestions or comments?

Thanks,

--...MARK_N1LO...--
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