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'a quarter wave'
>...how long is a quarter wave of wire...?
Welllll, as Richard says it can get complicated tryng to calculate.
(As near as i can tell the constancy (or not) of the speed of light
does not enter into it, but thats drifing off topic, sooo..)
Its a fact that when a '1/4 wave coil' is wound by, eg, radio
amateurs to function as an electrically short antenna, they start
with a _one_half_ wavelength of wire, then trim a little and
load a little.
Onna other hand, sucessful coilers tend (as near as i can tell)
towards 1/4 wave of wire, fudged by various factors. At a guess,
the principal difference between the 'antenna' and the coil is
the _aspect_ _ration_. Even the longest, skinniest, tesla coil
is shorter/wider than a continuosly loaded antenna. My impression
is that the evolution of coil design has been from tall skinny, to
short wide (eg: Tesla's Colorado Springs coil was Short/wide
fer sure...).
In any case, the objective, it seems to me, is resonance, not
0.250000000000... of wire. (which interacts with the other
discussion on why the 'top load' is used. Its for two reasons,
near as i can see:
1) A large terminal is the ONLY WAY _any_ one has found
to get large voltages to 'stay put'. (If someone knows of
another, that works, speak up. ) (I suspect that
many cases of 'top terminal makes coil not work', are
misdiagnosed, since the breakout voltage has been raised
THE SYSTEM needs to be retuned (also because it has been
detuned.)
2) The top terminal adds capacitance, hence, typically
allowing/requiring a shorter (electrical) secondary
(or, alternately) allowing (requiring) running at a lower
frequency, once the top terminal is in place.
regards
dwp