RE: RF ground connection

["sundog" <sundog-at-timeship-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi All, Kurt

  I wouldn't say it's a necessity, but the RF ground current can get quite
substantial with a big coil.  I believe it's because you're dealing with RF,
and the skin effect, so by "heavy" cabling, I believe "more surface area" is
more precise.  Probly much to the disdain of those on the list, I simply
sand ~3" on the secondary base lead (the 5-6" of wire hanging off) and wrap
that repeatedly around the 3 wire Romex I use for ground.  It works good for
me, maybe because my ground itself is really good.  I can see what you mean
about basically running 22 awg into a piece of 8ga welding lead, but I'm
pretty sure if you substituted a length of that 22awg wire for the welding
lead, you'd see a decrease in performance.  For my larger coil, Dave helped
me get a more oubstantial and robust connection for the ground.  But even
then, there's almost 3" of bare thin-gauge wire in contact with the
attaching point for the RF ground, so it's got a good healthy amount of
surface area to conduct over.

  Plus, I use the RF ground for the tranny cases, and line filters.  If the
tranny shorted to the case (bite my tongue!), I'd want the ground connection
to take the full 120v30A brunt of it and pop the breaker, instead of
trusting the house ground.  A piece of 22awg wire under 120v30+A will just
pop (trust me on that;), whereas the romex just gets warm for a second
before the garage plunges into darkness.  Oopsie....

   So do ya have to use mega-cable? Nope.  I'd suggest a nice healthy amount
of surface area for those RF electrons to crowd onto, tho.

Just my $.02 :)
									Sundog
-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, September 15, 2000 10:09 AM
To: tesla-at-pupman-dot-com
Subject: RF ground connection


Original poster: "Kurt Schraner" <k.schraner-at-datacomm.ch>

Hi all,

it is common practice to ask for a heavy connection of the
secondary base to the RF-ground. But how big is the need? - If we
have a secondary, it is probably wire AWG 26...22...or, if it's a
big coil: AWG 17. This seems to be big enough for the RF-current
of probably some 5...30A RMS (not pulse!) of RF. But suddenly,
after leave of the lower end of the secondary, the recommendation
goes to use copper-strap or -tube or very heavy cable. I
understand, fixing the earth potential is somehow like a vice,
fixing a spring for resonant oscillation (wrong analogy?). But
how big is the influence on coil performance (=sparklength)? - On
the way from the lowest secondary turn to ground, we encounter
several impedances: lowest turn to ground line - ground line (
Length=?) - line to ground. What are the relative impedances?
Some coils are even operated with counterpoise, without 'real'
ground connection (capacitive grounding). How small, a ground
connecting line can be, without sacrifying performance? Excuse my
ignorance, not having checked the archives! Is there any
quantified experience? Any help appreciated!

Kurt