Re: BIG counterpoise

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Mark,

At 10:17 PM 12/8/2002 -0600, you wrote:
>I have a similar grounding issue.  The coil I built and left my physics 
>department has gone
>through 2 transformers, with properly set safety gaps and 
>TerryFilter.  (Ok, so the ground
>wasn't attached to the TerryFilter the last time.)

I am a little surprised anyway.  The "me" filter :o) should have still 
provided some protection even without a ground.  You may want to add input 
fuses if you don't have them already.  I worry about the NST shunts 
saturating and the NST drawing very high currents.  Since your running it 
LTR I don't think over voltage should be a problem (the filter should still 
protect against that anyway).  It could be RF ripping through the 
ungrounded filter, but I would add a fuse and see if the NST is going 
nuclear on input current.  This may be really true if the coil's power were 
turned on without the gap running.  But, the safety gaps should still keep 
it under control...  I guess I don't see what is hurting the NSTs here...

>The coil is 6" secondary with 15/90 input,
>SRSG, LTR MMC (Panasonics - long before the GeekMMC).  It is run almost 
>exclusively
>on the third floor of the physics department on the inner "square" of the 
>building
>(surrounded by classrooms, offices, or a hallway).  I've used mainly a 
>cold water pipe for
>RF ground, which seems to work, though I have no clue if the pipe is metal 
>all the way to
>the ground.

If the pipe goes to plastic (unlikely in a commercial building) then the 
ground rod may be no more than an antenna.  Simply ohm between the pipe and 
the AC ground which should have very low resistance between them.  A small 
counterpoise may be great here.

>I've also used a big flexible steel conduit that was housed the lab power 
>supply
>feeds from the monster regulated power supply in one of the back 
>rooms.  There was no
>performance difference between the two.

"Flexible" (big spiral) galvanized steel (bad skin effect RF conductor) may 
not be a great RF ground especially at the higher RF noise 
frequencies.  But probably "ok".


>Running a long dedicated ground out a window isn't an option for a variety 
>of reasons.  The
>best option is a counterpoise.  But I'm concerned that the concrete floor 
>40 feet above soil
>will be a good enough reference point to keep the counterpoise voltage 
>sufficiently low.  I'd
>hate to lose another transformer or even the spark gap motor due to 
>excessive ground
>potential....

The concrete floor is filled with rebar and is connected to big iron 
beams.  It is "sort of" conductive, but a counterpoise (just a little one) 
to contain the RF stuff should do great here.

Cheers,

         Terry



>Mark Broker
>Chief Engineer, The Geek Group