Re: Counterpoise question

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

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

In a message dated 4/9/01 2:20:07 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes: 


>
> > Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" 
> <yevaud_new.uk-at-excite.co.uk> 
> > 
> > Hi all - 
> > 
> > A recent post mentioned the use of a counterpoise. I'm in the middle of 
> > building a 1kW Tesla Coil and, when it is finished, have plans to 
> > demonstrate it to my physics students. However, finding a decent RF ground 
> > in the lecture theatre is not going to be easy so I was wondering whether 
> I 
> > could get away with using a counterpoise? Not having used one before, I 
> > hope you won't mind some pretty basic questions: Can I get away with using 
> > one at 1kW ?  If it is made out of aluminium foil spread out over the 
> > lecture theatre floor, how many square feet of it (roughly) would I need ? 
> > To what do you connect the other things that would usually be connected to 
> > the RF ground...NST core, safety gap etc....to the counterpoise as well ? 
> > Does the counterpoise really need to be connected to the mains ground as I 
> > think I read in one post or do you just leave it capacitively coupled to 
> > the ground ? 
> > 
> > With thanks, 
> > 
> > Alan. 
> > 



Hi Alan! 

        An electrical counterpoise is a conductive surface under the coil 
that "looks like"  a ground to the secondary. If you can't reach the ground 
with a reasonably short wire, this may be a better way to go. One made of 
many thin wires placed radially is claimed to be better, because a solid 
surface (foil, flashing, etc.) is home to significant eddy currents. From 
what I have seen, it should be at least as large in diameter as your primary 
winding or strike rail. I personally would not connect anything from the 
secondary side of a Tesla coil to any mains connection in any building 
containing any equipment owned/used by other people. 
Hope this helps, 

Matt D.