Re: RF ground connection

["davep" <davep-at-quik-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

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

> it is common practice to ask for a heavy connection of the
> secondary base to the RF-ground. But how big is the need?

	A matter for experiment, doing them well is tricky.
	One thing the early wirelss guys found was the need
	for a good RF ground.  Tesla work matches that, at moderately
	lower frequencies.  Tesla demonstrated the
	advantages of a good ground in Colorado Springs...

> - 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.

	The base of a quarter wave coil has a current peak, analagous to
	the voltage peak at the top.  Largish currents.  Larger than
	expected.  Also (as noted) to some extent its a matter of big
	wire, for reducing skin effect related losses (which go as the area).
	(Consider using copper pipe, put the conductivity where its needed.)

> But suddenly, after leave of the lower end of the secondary, the
>recommendation goes to use copper-strap or -tube or very heavy cable.

	If the coil (assuming grounded, most typical) is not WELL
	grounded then losses occur here, as well as currents finding there
	way to Un Pleasant places (cf comments about increased rfi...)

	Since this IS RF (albeit LF) capacitance, including stray, can
	provice a 'ground' invisibly.  Doing careful experiments
	in this area is challenging.  And the importance of the ground
	increases radically as the power goes up.

	A poor ground looks like a high resistance, which spoils the
	Q, the goodness of the resonance.  The resonance creates the
	voltage peak.  A good ground should raise the voltage.  (If the
	coil breaks out before the limit implied by the ground, the
	influence of the ground being sub optimum may not be
	obvious.)

	best
	dwp