Frequency of 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>

Today I hooked up a flat plate antenna through a 20dB attenuator to an HP 5328A
universal counter.  My flat spiral secondary measured 260KHz as its best
resonance frequency when tested with a signal generator and voltmeter.  The
frequency counter shows resonance in a range of 24KHz to 32KHz while the coil
is actually operating.  Does anybody know what this means?
 
Also, using the same antenna system and feeding into an oscilloscope, a nice
pulse appears on the screen.  However, there are clearly two traces in the
pulse.  I can manipulate the traces by adding the 30" flat plates to the flat
spiral secondary terminal connection.  Adding a 30" plate 10" above the coil
causes the positive trace to ring longer.  Moving the 30" plate 20" away from
the coil makes the positive pulse ring longer yet.  Having a plate on both the
bottom and the top causes both traces to ring longer.  But I haven't yet made
the pulses ring in unison.  I'm going to add some degrees of tuning by winding
a bare copper primary and connecting an 8 point spark gap.  
 
If anyone knows why the coil appears to be running at a lower frequency than
the tank circuits are tuned, I'd like to learn why.
 
Dave