Re: Spaced Coil measurements.
> Original Poster: "B**2" <bensonbd-at-erols-dot-com>
> Hi Malcolm, All,
> Using your measurements I get 18.25 pF from Medhurst's formula. I
> plotted your data in Excel as 1/(f^2) VS C according to Howe. A
> linear trend line fit to the data crosses the axis at about -50 pF.
> 50 pF seems a bit high. You gave Ns = 38 turns for the whole coil?
Your value of Cself would be closer than mine. I guestimated a figure
for Medhurst's H factor from the h/d ratio. The plot seems to suggest
that something's not quite right with this coil. I'll double-check
the turns but 38 is what I wound I'm sure. This gives around 1.1 TPI
with relatively tiny Dwire.
I'm going to follow up on Terry's suggestions this weekend to get
more data. The idea is to hold h/d constant (and hence Cself if
Medhurst holds good) while progressively reducing turns to 1. I might
not get to 1 as the frequencies will get beyond the range of my Lo Z
signal generator rather quickly and I may have to resort to using a
higher impedance (transformed perhaps) RF generator. There was no
point in starting with a closewound coil. I think we all know the
results of doing that ;)