30MHz Spark Gap Testing - Is this real??
From: terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
Sent: Sunday, April 05, 1998 11:44 PM
To: Tesla List
Subject: 30MHz Spark Gap Testing - Is this real??
I believe that I have made a new and significant discovery regarding spark
gap operation. My experiments, which deal with the measurements of voltages
and currents in the primary circuit, have shown that the operation of the
spark gap is not that of a simple switch.
It is generally believed that when the voltage across the spark gap reaches
a certain level that current passes through the gap and super heats the air
creating a virtual short across the gap. This short remains in place until
the primary circuit losses energy and the super heated air region can no
longer be maintained. At this point, the resistance is believed to rise and
the gap "quenches" and the resistance returns to a very high level. Typical
measurements performed with relatively low bandwidth equipment more or less
have demonstrated this phenomena. Once the gap has closed, the current
through the gap is assumed to be a simple decaying sine wave.
When equipment capable of much higher bandwidth is employed this picture
seems to change dramatically. When one terminates a quality antenna into
the proper 50 ohm impedance the fundamental signal seems overwhelmed by
heavy noise spikes. This explains why a simple wire is often used as a
scope probe to receive primary waveforms as opposed to a higher quality
antenna system. The simple wire and its very poor impedance matching to the
input of an oscilloscope attenuate these noise signals so that only a nice
clean signal is left.
If one uses a high bandwidth properly terminated antenna, a series of noise
spikes are seen (my testing was done without the secondary inductor in
place). Careful examination will show these spikes appear as a series of
noise bursts that occur at the peaks of the fundamental frequency. The
power of these noise bursts is vastly higher than the fundamental waveform.
In my testing, I have found that these burst consist of ~50MHz signal bursts
that persist for about 100nS and then fall off to a much lower level. The
power of these bursts is remarkable. Early testing has shown that, even at
low voltage levels, these bursts may reach many hundreds of amps at the
~50MHz frequency. By far the most powerful burst is the very first one.
Typical scope photos often show this as a vertical line that occurs just at
the beginning of conduction. My equipment has not been able to measure the
level of this spike with great accuracy but it appears to be around 400 amps
which is remarkable considering the relatively low 2000 volt spark gap
setting. What is even more remarkable is that the current outside this
burst appears to be close to zero. In other words the full current in the
primary seems to be conducted only in these short bursts.
Others and I have measured nice sine wave currents in the primary system
before. So how can the preceding be true? I fear we have been tricked by
the low frequency response of the equipment we used and the classical
impulse response of those systems. These energy bursts can easily act as
pure impulses which will excite a low bandwidth system producing sine waves.
We may have only been seeing the heavily damped response of these current
What are the implications if this is true? If the primary circuit is doing
all of its work at ~50MHz and at hundreds, if not thousands, of amps at that
frequency, everything changes! The conductors must be short, wide, copper
strips. The capacitors must be able to withstand even greater stresses than
we ever imagined. And the spark gaps... who knows? This would imply that a
much better spark gap or other switching system may give much better
performance. EMI becomes a major concern. At 200KHz it is easy to
disregard EMI. At 50MHz all kinds of problems can arise.
I have written a paper on all this. It is available in Word 97 format and
as an HTML web document at:
Look at the 30MHz Primary Circuit Measurements section. You may want to
save the graphics and view them with a viewer to get the highest resolution.
The main page is:
I realize this is a rather dramatic change in the way we all look at
primary circuits. I have tried my best to confirm this. Unfortunately, I
seem to be rather alone in my ability to probe into these regions so
independent confirmation is difficult. However, I am confident that the
truth will be determined quickly. As far as I can tell everything appears
to be working properly and all the results I have seen make sense and appear
Comments are very welcome.