Re: School demo

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Hello....

(snips from Jim Lux)
> Actually, I beg to differ, the important capacitance is between the top
> load and the counterpoise, supporting the RF current flow through the
> secondary inductance.  

Your description sounds great to me, I might have been mistaken when I said 
the coupling is from counterpoise to earth. Given both views, maybe what's 
happening is a little of both? I mean, there definately IS capacitance 
between a counterpoise and ground........whether or not this is the 
"capacitor" doing the work or not, I don't know.

> Putting the counterpoise there reduces the 
> coupling to the earth ground.  without a counterpoise, the "other plate" 
> for the top load capacitance is the ground, the walls, anything 
> conductive that happens to be near the TC (like you), and the RF 
> current flows through it (generally a "bad thing", when the path 
> happens to be your feet, or the AC green wire ground, the garage 
> door opener wires, etc.)

I do know that I was able to draw hot, bright sparks (typical of discharging 
any capacitance) from the counterpoise to a real live RF ground. That tells 
me there is a lot of voltage there, and that tells me this is not the best 
thing to do when running a coil at a school. I set this experiment up 
intentionally to prove that a dedicated RF ground is much better than a 
counterpoise.

Granted, a bigger counterpoises were working better. At the time I was using 
a smallish (2.5 foot square) counterpoise for a 3" coil running about 500VA. 
MUCH larger counterpoises (more aluminum foil ; ) were making a good deal of 
difference................but, it's been my experience that you have to use a 
HUGE counterpoise to lower the voltage enough to *at least* not arc out and 
get you. All of the counterpoises I've tried have had corona all over the 
edges. Lots of voltage.

My point: I don't think any *practical* size of counterpoise will ever be 
safe. Of course, one stretched out over a mile will work excellent......but 
that's not practical ; ) I'm keeping in mind that running a coil for the 
public (especially at a school) requires a practical setup usually. That's 
why I'm not really "for" the counterpoise in this situation.

Take care,

Justin Hays
KC5PNP
G-3 #1150
Email: pyrotrons-at-aol-dot-com
Website: www.hvguy-dot-com