[Prev][Next][Index][Thread]
Re: Optimal toroid elevation
Hi all,
Earlier today I wrote:
On 28 May 00, at 20:24, Tesla List wrote:
> Original Poster: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz>
>
> Hi all,
> You might care to take this with a grain of salt right now but I
> have something for you all to consider when determining terminal
> capacitances:
<snip of Bart's measurements>
> It is worth bearing in mind that using Medhurst's C and measured
> frequency with added top hats is not going to give the correct
> answer for Ctop (or Ctot) since Medhurst's C is not the intrinsic C
> for the coil. I have a preliminary indication that adding a top hat
> might well add more capacitance than is currently inferred from the
> frequency measurements. Later today I will do a measurement on
> my work coil (which clocks in at 67pF-odd intrinsic C vs Medhurst's
> 19.? pF and post the comparative results with and without the
> topload I am presently using.
OK - I pulled the 10" resonator off the coil and hooked LC Analyser
to it to re-measure intrinsic C. This came to about 70pF. Disturbed
by the meter jumping between 69 and 72 pF I decided to turn the
fluorescent lights in the workshop off and immediately measured
around 50+pF. It is obvious that I cannot do any meaningful or
definitive measurements save frequency and inductance without the
isolation I mentioned above so further msmts are on hold until I get
the space. However, I did plonk the topload I've been using on and
measured an increase of 20pF odd. That is a far cry from the
additional 7 pF or so that I calculate using F and Medhurst in the
standard resonance formula. While the figures are far from reliable I
know they are indicative and echo what I saw the other night at
home. If the indications are anything to go by, it is obvious that
some rethinking of issues such as resonant modes, electrical length,
Vout etc needs to take place. It seems to further drive home the
point about Medhurst being a *recipe* and not much more.
Regards,
Malcolm