30MHz Spark Gap Testing - Is this real??

From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
Sent:  Tuesday, April 07, 1998 6:31 PM
To:  Tesla List
Subject:  Re: 30MHz Spark Gap Testing - Is this real??

At 01:24 AM 4/7/98 -0500, you wrote:
>From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]

>Hi Terry,
>            Fascinating post:
>First of all, one might approximate the gap as a short. In reality 
>and at "low" frequencies, it isn't really a short at all although it 
>can approximate a voltage sink, albeit not a super stiff one. It 
>does consume a considerable amount of power as evidenced by light, 
>heat and sound. One can also measure losses at some particular 
>current and width.

	I suspect the voltage and current waveforms are not out of phase during
these spikes.  In other words power is being dissipated.  I need to better
shield my high voltage fiber probe to test this.  I have some die-cast
enclosures on order to keep the spikes from messing with the voltage
dividers.  Now the probe signals are not reliable voltage wise.  At 50MHz I
am reaching the limits of the scope and such so it gets even more difficult
to determine exact phase.  I have tried to keep the voltage and current
sensors identical in every way possible to preserve phase information even
at these high frequencies.

>>     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.   
>The antenna is primarily picking up e-field noise isn't it? What does 
>a high BW current probe say?

	The current probe and the antenna match perfectly.  The fiber-optics add
some delay so the scope pictures don't line up but if you shift the waveform
over to account for the delay they match well (it takes about 33nS for the
light just to drag itself through the 10 meter fiber cable:-))   I need to
document this better.  As I went over my pictures I saw that I didn't have
the scope set right to show this well.


>But again, does this manifest itself as similar changes in primary 
>inductor current (not just over exceedingly short wiring paths)? I 
>suspect not for the simple reason that the inductance is rather 
>significant at such high frequencies. Still, I could be wrong.

	Good point.  At these frequencies who knows how the currents would appear
throughout the primary system.  No answers yet on this.  I bet it is really

>>     I have written a paper on all this.  It is available in Word 97
format and
>> as an HTML web document at:
>> http://www.peakpeak-dot-com/~terryf/tesla/experiments/experiments.html
>> 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: 
>> http://www.peakpeak-dot-com/~terryf/tesla/main.html

>Great post.