Re: [TCML] Inspecting a coil while running

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Steve,

You could simply insert a lead (a stiff wire about 4" long) into the end 
of your scope probe at a distance away and pick up the signals you want. 
It's not ideal, but most have performed their various measurements this 
way. There is an antenna designed by Terry Fritz to help with bandwidth 
and frequency response. It's known as the "plane wave" antenna. I built 
one myself several years ago and still use it for measurements. This is 
my rendition:
http://www.classictesla.com/temp/planewave.jpg
What you don't see are the bnc connectors on the back side which runs to 
the scope. I use the planewave antenna for various measurements when I'm 
looking at extracting a signal from the coil during operation or simply 
excited with a frequency generator.

Here is Terry's writeup which I worked from. If the link hangs, then the 
site is down, but only temporarily.
http://hot-streamer.com/temp2/PlaneWave.pdf

For bps type measurements, you'll get different techniques. For myself, 
I used the spark gap breakdown light. I set a fiber optic cable end in 
the gap and used the light to energize a simple light transducer. In my 
case, I used a Windaq data acquisition thing that plugged into my pc. 
But this signal could have easily gone to a scope.
http://www.classictesla.com/temp/light%20transducer%20board.JPG
And some of the bps signals captured:
http://www.classictesla.com/temp/bps_test_1560.gif

A current transformer is also very useful for measuring base currents 
(everything in the secondary is inside those signals). This is basically 
an air core coil in which the ground lead from the secondary passes 
through. Most CT's are equipped with a bnc connector to go directly to 
the scope.
http://www.classictesla.com/temp/CT%20001.JPG

Take care,
Bart







Stephen J. Hobley wrote:
> ...and another question. :-)
>
> I'd really like to take a closer look at some of the electrical signals operating in different parts of the coil while running. Is there any information on building devices that can safely couple an oscilloscope to coil components?
>
> Areas of interest are static spark gap timing, primary ringdown, first and second notches etc...
>
> I thought about maybe some kind of radio receiver arrangement, so that physical contact is not required - but I would interested in any other methods.
>
> Steve
>
>   
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