Re: Quarter Wavelength Frequency

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

To make a very long story short....

Consider how long it takes for current at the base of a coil to reach to 
top of the coil...

If it travels the length of the wire (say 1000 feet) then the wire "length 
idea" holds.

But here is the catch that changes everything!!!

The coil's turns are all magnetically linked to each other!!

So the current at the top of the coil doe not have to wait for the 
electrons to travel the length of the wire, but only the length of the 
coil!!  The effects of primary base current are magnetically linked to the 
top of the coil through a distance of only say 3 feet...  The coil is not a 
1000 foot long antenna.  It is a close wound inductor with the all the 
turns closely magnetically linked....

That simply is the "killer" the of wire length/quarter wave stuff...

Listen to Paul here!!!  He has studied this stuff to extreme detail!!!!

http://www.abelian.demon.co.uk/tssp/

Cheers,

         Terry

At 02:40 PM 7/9/2004, you wrote:
>Jared E Dwarshuis wrote:
>
> > we believe that an envelope exists between L.C.
> > resonance and wire length resonance.
>
>This seems to be where you're going wrong in your
>interpretation of your coil's behaviour.  LC resonance
>and 'wire length' resonance are two equivalent
>descriptions of the coil's resonant modes, and should
>not be thought of as two different modes of resonance
>capable of being excited simultaneously in order to
>produce beating or interference.
>
>A common factor in the two descriptions is the distributed
>inductance and distributed capacitance of the wire.  To
>proceed in one direction, you integrate these to produce
>overall equivalent 'lumped' L and C values for use in the
>'LC resonance' model.  Going the other way, you proceed to
>derive a propagation velocity for the coil (from 1/sqrt(LC)
>where L and C are the per-unit-length values), and so
>deduce the 'wire resonance' modes.   They are of course the
>same set of physical resonant modes in both descriptions.
>
>The distributed L and C of the wire depends strongly on
>how the wire is arranged with respect to itself and
>surroundings.   Both alter in a more or less complicated
>way when the straight wire is wound into a coil.  Therefore
>you cannot draw upon the reactances (and the corresponding
>resonances) of the original straight wire when interpreting
>behaviour of the wound structure, since the original straight-
>wire distributed reactances were completely lost when the coil
>was wound.
>
>During winding, the self inductance of a wire element is
>greatly increased by the presence of the neighbouring
>turns being brought up against it.   At the same time, the
>self capacitance of the wire element is greatly reduced,
>because it is now partially shielded by the adjacent conductors
>being at almost the same potential.   These two changes occur in
>approximately the same ratio, give or take a factor of 2 or so,
>resulting in the velocity 1/sqrt(LC) usually being within a factor
>of two each way of light speed.
>
>Now the claim that 'wire length' resonance and 'LC resonance'
>are occuring simultaneously as physically distinct resonant modes
>requires the coil to resonate with its wound resonance, while at
>the same time somehow 'remembering' the reactive properties that
>the wire once had when straight and resonating in accordance with
>those too.  If this were the case, it would be possible to observe
>the mode spectrum of a coil to be the union of the free-space straight-
>line original wire mode spectrum, plus the normal spectrum of wound
>'LC' resonances.
>
>This is never seen, instead we always see a single mode spectrum
>whose mode frequencies can be related (equally correctly) via an
>LC model or via a wire resonance model, back to the distributed
>reactances of the wound wire.
>
>A typical straight solenoid has a fundamental resonant frequency
>a little higher than that which the straight wire used to have.
>
>Using the example offered to Shawn,
>
> > Suppose we make a hypothetical secondary with 1000 turns of
> > 22 gauge around an 8 inch diameter pipe, Medhurst predicts about
> > 11.7 Pf.  Wheelers formula gives .523 Henry while the classic
> > inductance formula gives .594 Henry, then the self resonant
> > frequency of this coil would be between 240,000 and 260,000 Hz
> > But the predicted quarter wave wire length frequency is only
> > 118,000 Hz.
>
>Indeed so (*).  Now to be satisfied that only the 200kHz resonance
>is present, it is merely necessary to sweep the coil with a
>signal generator to see that there is no mode lower than this, and
>in particular there will be no change in the coil's dynamics as
>you sweep through the frequency that the wire used to resonate at
>before it was wound.
>
>(*) For this coil, assuming 28" wound length and mounted 4"
>above a ground plane, base grounded, I get 198kHz for the 1/4 wave,
>50.8mH for DC inductance,  41.7mH for the lumped equivalent
>inductance of the 1/4 wave resonance, 15.5pF for the corresponding
>effective lumped capacitance, and irrelevantly, the Medhurst
>capacitance would be 12.7pF.
>
> > The coil operating at 118,000 Hz will have much larger
> > amplitudes and be easier to tune.
>
>We're supposing here that you mean pulling the 200kHz resonance
>down to 118kHz by end loading with topload capacitance.  But there
>is no evidence that any special behaviour occurs when this
>is done.   We know that to do so results in a satisfactory
>proportion of stored charge in the topload of the TC, but there is
>no reason either experimental or theoretical, to suppose that
>the original straight line wire length resonance is the optimal
>target to aim for.  If you were to study the dynamics of this
>hypothetical coil in the region between DC and the resonant
>frequency of 198kHz, you would not be able to find any measurement
>which does not vary smoothly and indifferently as you pass
>through the frequency corresponding to the resonance of the
>original straight wire.  Likewise if you top-load the resonance
>down to lower and lower frequencies - again you will not see
>any measurement reach any sort of a peak or optimum as you
>load down through the frequency of the original wire resonance.
>
> > When we run our full wave devices we can only get them to work
> > at the wire length frequency (or multiples).
>
>Perhaps so.  It is quite feasible that winding into a toroidal
>coil just happens to leave a unity velocity factor.
>
>Or do you mean that the coils wont perform unless you apply
>additional reactance in order to pull the natural resonant
>frequency of the toroidal coil down to or up to the frequency
>that its wire used to have before it was wound?
>
> > Changes in top end capacitance do not destroy the resonance;
>
>You mention top-end capacitance, so you have, it seems, added loading.
>
> > ...it appears to be fixed by the primary L.C. and the wire length
> > of the secondary.
>
>Ok, thats fine.  It might suggest the resonant modes you are exciting
>are not strongly coupled to the top capacitance, ie the top-C is
>perhaps near a voltage node?  Without data we can only do futile
>speculation.
>
> > When we ran up the Levi configuration for the first time we got
> > a slow beat frequency between the two coils (a slow cycling of
> > spark length).
>
>You must look for a more realistic explanation for this beating, one
>which doesn't require radically new physics.  I took a look at
>the web page
>
>  http://people.emich.edu/jdwarshui/groundless.html
>
>which gives a few hints as to what you're doing, but it doesn't give
>anything like enough info to go on.   Referring to the arrangement
>which produced the beats, a circuit diagram would be helpful, and
>some indication of how you are driving the coil.  It is difficult
>to draw any conclusions from the info given so far.
>
> > Yes the velocity appears to be very close to, if not exactly,
> > the speed of light. How close? couldn?t say. We have to base our
> > conclusions mainly on observations and calculations.
>
>If so, then you will have measured the wire length, and measured the
>resonance frequencies, and then simply calculated
>
>   velocity (along the wire) = wire_length * resonance_freq
>
>for the full wave resonance, etc.
>
>The coil configurations that you're working with look to be quite
>interesting and complicated and will be difficult to study. The
>fact that you're using three coils, at least two of which appear
>to be floating, and two of which may be capacitively as
>well as inductively coupled,  makes things trickier still.
>The whole system should be measured and studied carefully before
>coming to any conclusions about which resonant modes are being
>excited to produce the observed spark behaviour.  The explanations
>given to us at present seem to be rather vague and partly
>based on a familiar myth.  Plus they are not supported by any
>measurements, circuit diagrams and dimensions, and so on, which
>leaves us, temporarily I hope, unable to offer more reasonable
>alternatives.
>
>I think we would like to see first some basic studies of the
>toroidal coil resonances themselves, ie for each coil in isolation
>we would want to see what its mode spectrum was: the resonant
>frequencies, and for each resonance the locations of voltage and
>current nodes.  This in itself would be quite a challenge, because
>the spectrum and the node locations will be sensitive to symmetry
>and balance of the toroid with respect to ground, and so on.
>You might be able to observe mode splitting due to asymmetry,
>etc.  And you might even be able to obtain a slowly rotating
>pattern of nodes by careful excitation of one of these coils
>at two frequencies.
>
>Let me thoroughly recommend studying to death just one of these
>toroidal coils before even considering exploring its coupling to
>other coils.  If this is not done, then when you observe
>interesting behaviour of the coupled system, you will have
>no firm basis upon which to offer more than speculative
>explanations.  I'm sure many list members would, like me, be
>interested in a close look at this type of coil.
>--
>Paul Nicholson
>--