Mark Conway wrote:

 MC> Here's a question that I have been wandering for sometime 
 MC> but I can't seem to find any books to answer it. The question 
 MC> is why is a good ground so essential for Tesla coil work? 
 MC> Why won't a Tesla coil produce nearly as good a spark if it 
 MC> doesnt have a good ground?

 MC> I know that the earth acts as a good conductor that can carry 
 MC> away excess charge from an object but I cant see how this would 
 MC> help in Tesla coil work. I guess its the same question as why a 
 MC> radio transmitter needs a good earth to transmit efficiently (a 
 MC> ground plane?) I have looked for answers in the ARRL handbook and 
 MC> lots of others but I cannot find anywhere a reference that explains 
 MC> about grounding. 

 MC> Anyone out there know?   Cheers, Mark Conway
 MC> Internet: mconway-at-deepthnk.kiwi.gen.nz

OK, your resonate coil is generating a very large voltage at the 
top of the coil, the location of the 1/4 wave voltage peak. There 
is not a whole lot of current at the 1/4 wave location both in
theory and in practice.

The base of the coil however is a "nul" voltage point, or ground
potential. There is not a whole lot of voltage here, but RF current
is plentiful and heavy, both in theory and in practice.

The top and bottom of the coil have inverse current/voltage relation-
ships. Top, high voltage, low current : bottom, high current, low
voltage. Total energy output ( V*A ) must be equal from both ends. 

The ability of the coil to process power requires that the current
at the base wire be removed as quickly and efficiently as possible.
If this current is not removed and a high impedance ground path 
exists, then the coils ability to produce very high voltage is limited.

Also, this RF current will "crawl" along the floor or other conductors
if it is not grounded directly to earth via the shortest, lowest 
impedance path possible. This "crawling" RF is a significant
source of RF interference/contamination as it will get into the house
wiring via the 60 cycle ground path.

The house 60 cycle ground wire also grounds your computers mother-
board, TV set, radio, and what other expensive electronic equipment?

Richard Quick

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12