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Re: [TCML] Confusing Between 1/4 and 1/2 Wave Coil
Cole Awesome-Jordan wrote:
Hi, I've had a bit of free time recently and i decided to go digging
for information on bipolar coils and the difference between 1/4 and
1/2 wave coils.
And I read this
http://www.pupman.com/listarchives/2004/January/threads.html#00804
however this got me quite confused on the subject. When you calculate
a "normal" coil with kHz=1/(2*?*L*C) is this half or quarter wave?
It's half isn't it?
And if you have a bipolar coil that is 1000 turns of 26 gauge magnet
wire (55.25 turns per inch) and the form is 2.375" by 18.125"
(approx.) what is the frequency? Because I've been getting all sorts
of answers some say multiple the frequency by 2, another said
1.38-1.4, and a really odd answer I found of 2.6 somewhere.
Any help is greatly appreciated.
Whoever invented the name 'quarter-wave coil' really confused the
subject for a lot of people. This is a supposed analogy to a grounded
quarter wave antenna fed at the bottom - the maximum voltage appears at
the top. A coil wound with a 'quarter wavelength of wire' will always
have a resonant frequency signficantly below the mythical frequency for
which the wavelength is assumed. A straight quarter wavelength of wire
would be resonant in principle but that would no longer be a 'coil'! I
forget exactly what Tesla wrote on the subject but I think he was guilty
either of bad think or bad writing - he should have known better.
Best to talk about 'coils with one end grounded and high voltage at
top' or 'coils with the center grounded and high voltage at the two
ends'. Sort of a very rough analogy to quarter wave and half wave
resonance but rough at best. Any practical coil has a height to
diameter ratio less than an extreme of about ten times and will be a
tiny fraction of a wavelength high. This means it's an exceedingly
inefficient radiator so any analogy to an antenna is pretty tenuous.
Ed
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