RE: How to Tune a Flat Spiral Coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Paul,

>Connect things up as

             Resistor
 [HP465A]----\/\/\/\/\/----------o> to outer coil lead.
     |        100 ohms         |
     |                    [AC V meter]
     |                         |
     ----------------------------o> to earth connection

>leaving the center terminal unconnected - I'm assuming here that you intend
to ground the outer end(s) of the coil during operation, so that the HV is
developed at the center.

Using the setup you prescribed above, I measured 345KHz as the resonant
frequency on the single wound coil.  This is to the outer lead of the coil
and to earth ground.  When out of tune the voltage reading was above 20V.
When tuned to 345KHz the voltage was down to 1.7V.  On this coil, the
primary was in place and one of the ends were grounded.

When measuring the wye coil using the same technique, I got a resonant
frequency of 325KHz.

> The 100 ohms resistor is not a critical value, try anything from a few
tens of ohms up to a Kohm or two,  whatever gives a
decent dip on the meter.

I used a 470 Ohm resistor.

Dave