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Wire Length, footinmouth disease...


>>>> That is: a one meter wire will be resonant
>>>> at 4 meters.  (call it 70 MHz, roughly...).  But.  Take that same wire
>>>> and wind it onto a single layer coil.  It Now "looks" "longer".  It will
        >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>^^^^^___ARGGGGGH!!!
>>>> now resonate at (roughly) 2 meters (call it 144 MHz...8)>>). 
>A) I didn't know that.  In fact, I have never heard it.
	Its not commnly bandied about, simply because MOST people in the bizniss
	don't do resonators that way.  I stumbled on it in some ARRL Antenna
	discussion...

>Perhaps that is why my second coil never gave a spark more than 1/4" long.
	Maybe.  Maybe something else.  Would need to know more about the coil.

>So what you are  saying is in essence that one should wind a coil with a
>length of wire  approximately 1/8 the wavelength of the desired frequency?
	No.  I sat there last night and stared and stared and i KNEW i was
	gonna blow it.  And i did.  The wire wants to be roughly a half wave, to
	resonate as a quarter wave.  And this is all "Aspect ratio" (height/dia)
	and turn spacing and phase of moon dependent....  But a half wave of
	wire will bring the coil a lot closer to resonating like a 1/4 wave
	than a 1/4 wave will....  The quoted text is accurate.  The half wave
	of wire (at 144) resonates like a 1/4.

>B) If the wire "looks longer", wouldn't that make it resonate at 8 meters and 
>(say)35MHz?
	THAT is what i said wrong.  THANKS for crystallizing it.

	  Once Wound It Looks Shorter,

	1/2 wave of wire, wound as a solenoid, "looks/acts" like a 1/4 wave.
	(subject to lotsa adjustments, as above..)

	My view is pick a target frequency (or length).
	Wind away.
	MEASURE.  use signal generator, sweep generator, spectrum analyzer
	(HAH.  We should be so lucky...)
	(MY reading is that m,uch of what Tesla was doing in C Springs was,
	with somewhat, ahhhhhhhh, simplistic, equipment, verifying the
	frequencies of each element in the design & getting them matched.

	See how close, then start doing the math for the rest of the system.

	If the only objective is "lotsa voltage" (and itsa fun objective),
	then "all the wire" (subject to size of coil form, etc) and let the
	frequency come out where it likes.  Then match the primary to that.

	If operation on some particular frequency is desired, for other
	reasons, then aim for that via the "1/2 wave" rule and go from there...