Re: Quarter Wavelength Frequency

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Jared,

On 5 Jul 2004, at 11:28, Tesla list wrote:

 > Original poster: Jared E Dwarshuis <jdwarshui-at-emich.edu>
 >
 > Hello my name is Jared Dwarshuis and my friend?s name is Lawrence
 > Morris. We have been experimenting with wire length resonance (as well
 > as two part resonant transformer designs). We have found that matching
 > wire length to L.C. is critical to the operation of our integer
 > wavelength coils.
 >
 > We use an inductor that is wrapped around a donut or toroidal form,
 > because this inductor has no ends. It is the closest possible fit to
 > the derivation of the classic inductor formulae L = uo Nsqrd Area/
 > length. Because we have formed our inductor from a single loop of wire
 > we have a boundary constraint, this coil can now only form integer
 > wavelengths which it does very nicely, at even multiples of the
 > fundamental wire length frequency.
 >
 > It may be the case that cylindrical coils can deviate enough from the
 > ideal inductance formulae to cause discrepancies between wire length
 > and L.C. resonance, or perhaps current nodes are not exactly where
 > people think they are, and this has lead people to believe that wire
 > length has no significance (an understandable mistake).

      In my experience (obviously limited to what I have done) it is
apparent that cylindrical coils *do* deviate in the manner described.
I have yet to find a single case where they do not and an
investigation I conducted at a time when a multitude of wirelength
formulae were being touted as being *the formula* to use were, at
best, applicable to a very limited set of circumstances (e.g. a
particular coil geometry, H/D ratio etc.). Some appeared not to work
for any case. (Well they were all different and couldn't possibly
have all been correct could they?)
      I find it difficult to reconcile the lack of a single example of
a helical coil obeying the case you describe as a mistake. I have yet
to observe more than one outstanding resonance in a bare helical
resonator and that resonance has always been at a frequency
considerably above what you would expect if you considered the
wavelength of the wire stretched out. Tesla himself repeatedly ran
into the conundrum as detailed in the Notes.
      One can of course add topload capacitance to make the coil
resonate at its "1/4 wavelength" and I have done that with several
coils. I have not observed any special properties appearing or
significant performance gains when this is done. That is not to say
they don't, just that any that do appear don't seem to make themselves
outstandingly apparent. I am more than happy to have my thinking
corrected by a single, demonstrable, repeatable counterexample as I
am always happy to learn more and correct past errors.
      Your toroidal coils I would regard as a quite different
configuration as you appear to, yes?

Malcolm

 > When we match the L.C. frequency to the wire length frequency we
 > believe that it minimizes interference between the two distinct
 > resonant energy storing mechanisms. Clearly L.C. resonance occurs in
 > systems that ignore wire length (such as the primary inductor), but
 > when the wire length is also considered in design, the dynamics
 > change. Our experiments indicated that it was impossible to find a top
 > end capacitor pair that would kill the wire length resonance entirely,
 > so we are inclined to believe that when your primary is tuned to the
 > wire length, the wire length resonance will be the dominant energy
 > storing mechanism.
 >
 > Check out http://people.emich.edu/jdwarshui/ to see our articles
 > describing the above in greater detail.  We would be happy to respond
 > to polite inquiries on these matters. If you are a serious coiler
 > living near Southeastern Michigan or just a local kid and would like
 > to see the Levi?s configuration in operation, send us an e-mail
 > jdwarshuis-at-emich.edu.
 >
 >
 >
 > Tesla list wrote:
 >
 >
 >  >Original poster: "Anthony" <ant17-at-optushome-dot-com.au>
 >  >
 >  >hi guys can anybody tell me how to calculate secondary quarter
 > wavelength
 >  >resonant frequency not just the standard resonant frequency
 >  >
 >  >
 >  >
 >
 >
 >