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Re: [TCML] Scoping Quench



Just wanted to throw this image out there also as it is a real scope waveform and may help you better realize what your looking for and looking at. This image was capture by Richie Burnett.

http://www.classictesla.com/java/script/notch2.jpg

Regards,
Bart

Bert Hickman wrote:
Hi Greg,

There's no need to probe your primary circuit in order to measure quenching performance. You can tell exactly when your coil is quenching by simply connecting your scope to a small wire antenna that's placed well outside of the sparking range of your coil (see John Freau's earlier post). You'll need to carefully set up your scope's trigger and timebase so that you can view a complete bang on your scope every time the gap fires. When set up properly, you'll see one or more sine-like RF envelope "humps" that progressively become lower in amplitude. By counting the number of humps on the secondary waveform, you can directly determine when your primary gap is quenching.

If your gap fails to quench, bang energy will continue to cycle back and forth between primary and secondary LC circuits, continually losing energy all the while. Once the gap quenches, the energy interchange process stops, and all the remaining energy becomes stranded within the secondary circuit. The remaining energy then decays within the secondary circuit (ideally mostly through leaders/streamers). If you could achieve a single-notch ("perfect") quench, you'd simply see a single secondary-side ring-up followed by a much slower decay (from Richie Burnett's excellent site):

http://www.richieburnett.co.uk/quench1.gif

If your gap quenched on the 2nd notch you'll see two secondary peaks, with the secondary decay occurring just after the 2nd peak. And so on... Here's an example of 3rd notch quenching from Richie's site:

http://www.richieburnett.co.uk/quench2.gif

I also agree with John - "perfect" single-notch quenching is not essential to obtain excellent coil performance. A given spark gap coil will show considerable quenching variation based upon the operating power level, degree of streamer loading, coupling coefficient, etc. You'll also see significant quenching variation from bang to bang even at a fixed power level, especially when using a static or asynchronous rotary spark gap. A very well written in-depth discussion about quenching can be seen on Richie's site:

http://www.richieburnett.co.uk/operatn2.html

The bottom line:
There is simply no need to risk your scope (or potentially your life) trying to measure your primary circuit when a simple secondary antenna will provide you with similar quenching information.

Bert
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