secondary waveforms

To: tesla list <tesla-at-pupman-dot-com>
Subject: secondary waveforms
From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
Date: Thu, 13 Feb 1997 13:53:10 -0800
Subscriber: sgreiner-at-mail.wwnet-dot-com Thu Feb 13 22:02:04 1997

Hi All

I have wound a small toroid with a few turns of wire which are connected
to an oscope. The grounded lead from the TC secondary passes thru the
toroid and then to ground. Purpose, I thought, was to look at the
wavfeform of the current in the secondary during operation. I have
waveforms but not quite what I expected.

The waveform does indeed exhibit a decreasing envelope which is
synchronized with spark gap. The oscillations within the envelope are
not pure sine waves. They appear to be a mixture of probably two sine
waves of about equal amplitude, one being about 2x the frequency of the
other.
This gives a waveform which appears to be one sine wave with a major dip
in each peak which goes almost all of the way to zero. I assume this is
about what two frequencies, one being 2x the other would end up to look
like. This implies, if true, that the secondary is ringing at two
different frequencies. The lowest frequency appears to be about 290khz
which is approximately the unpowered resonant frequency.

The question: What am I seeing? I assumed that the ring down in the
secondary would be sinusoidal at a frequency somewhat less than the
natural resonant frequency in the unpowered state. Should the ring down
be a single frequency sinusoid in a correctly operating TC? Most
write-ups seem to imply this. If this is the case, where is the second
frequency coming from and how does one get rid of it?

Some specs( unpowered):
Secondary
Fr=283khz with 8x26 toroid
Fhigh=301khz
Flow=227khz
240 turns  14" x 30"

primary: 5 turns .375"tubing  18.5" diameter, solenoid wound
Primary res freq=234khz
Cap: .021uf
Neon:15kv-at-120ma
discharge: 54" to 60" (room limited)

Thanks in advance for any comments

Skip