RF ground connection

["Kurt Schraner" <k.schraner-at-datacomm.ch> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

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