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Re: Wire length,resonance, and Q (fwd)
---------- Forwarded message ----------
Date: Fri, 22 May 1998 04:50:06 -0500
From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Wire length,resonance, and Q (fwd)
John and All,
Backing up for second;
I think most would agree that the 1/4 wave formula is not absolute for operation,
but, just as Tesla used the 1/4 wave calculation as a guide, when answering
questions for new coilers who are looking for the number of turns for a
secondary, I would suggest the 1/4 wave calculation, as it does put them right
into the operational ballpark. Would others agree on this?
Going forward;
This thread is always interesting when it comes up from time to time. The big
question which I keep asking myself is, "What are the optimum parameters?" as
John hinted towards. I wonder if there is really is an optimum. It appears that
each coils optimum setting is unique to the geometry, size, power levels, ground
plane, and a host of other variables.
Bart
Tesla List wrote:
> ---------- Forwarded message ----------
> Date: Fri, 22 May 1998 06:08:58 +0000
> From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Wire length,resonance, and Q (fwd)
>
>
> Jim, Malcolm, All -
>
> It is true that Tesla used quarter wavelength calcs as a guide, however,
> he also said that his Tesla coil would operate correctly at other
> frequencies provided the system was in tune. The reason is that he believed
> the TC was an air core resonant transformer. This means that transformer
> theory is involved and that means electric and magnetic fields.
>
> It should be noted that electromagnetic fields (Hertzian waves) propagate
> at the speed of light. This is not true of electric or magnetic fields which
> are perpendicular to the direction of propagation of electromagnetic fields.
> This confuses coilers and many others the same as the fact that energy
> transfer by magnetic induction is always at 100% transfer. Tesla said that
> his TC did not operate with Hertzian waves.
>
> As an example assume a 1000 ft length of wire for the TC secondary coil.
> This has an approximate quarter wave resonant frequency of
>
> Freq = 246000/Ft = 246000/1000 = 246 KHZ
>
> A typical TC with 1000 Ft of sec wire would have about 12 mh inductance
> and about 9 pf of self capacitance. The resonant frequency would be
>
> Freq = 1/(6.823 x sqrt(LC)) = 1/(6.823 x sqrt(12 x 9 x 10^-15) = 484 KHZ
>
> This is almost twice the straight wire resonant frequency. However, if the
> pri LpCp equaled the sec LsCs the system would be in tune and would produce
> a spark length dependent on the input watts and the overall efficiency.
> There are many other combinations possible.
>
> This TC would also work at the 246 KHZ resonant frequency using a 6" x 22"
> toroid with an effective capacitance of 26 pf.
>
> Cap = 1/(39.5 x 246000^2 x 12 x 10^-3) = 35 - 9 = 26 pf
>
> This TC would work at many frequencies by varying the toroids but the
> frequency would never be greater than about 445 KHZ using a typical sec coil
> of 3 or 4 to 1 and 1000 ft of wire. It is obvious that the TC works as a
> transformer and must be designed with that in mind. So far the results of
> random testing by coilers makes it difficult to find the proper combination
> of parameters for an optimum coil.
>
> John Couture
>
> -----------------------------------------------
>
> At 08:59 PM 5/20/98 -0600, you wrote:
> >
> >
> >---------- Forwarded message ----------
> >Date: Thu, 21 May 1998 08:56:11 +1200
> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >To: Tesla List <tesla-at-pupman-dot-com>
> >Subject: Re: Wire length,resonance, and Q
> >
> >Hi Jim,
> > My explanation FWIW:
> >
> >> From: bmack [SMTP:bmack-at-frontiernet-dot-net]
> >> Sent: Monday, May 11, 1998 9:43 PM
> >> To: tesla list
> >> Subject: Wire length,resonance, and Q
> >>
> >> To all,
> >>
> >> When Dr. Tesla made initial coil designs, he often resorted to quarter
> >> wave length calculations as a guide. My early impressons of this was
> >> that it was the upper boundry for the physical length of wire that could
> >> be used. Since, however I found that this is not neccessarily the case.
> >>
> >> The most intriguing thing is the cases where the coil resonates at
> >> frequency HIGHER than the wire length alone indicates! Malcolm made
> >> a passing refence to this in one of his recent posts as well. Preliminary
> >> quick experiments indicate that the coil geometry has alot to do with it's
> >> ultimate resonant frequency apart from the length of the wire. Really
> >> bizzare things happen when the aspect ratio is below 0.1.
> >>
> >> According to conventional physics, (let me know if I missed something)
> >> a charge and it's attendant feilds will propagate faster in a straight
> >> wire
> >> than in a coil. It follows that the coil should always resonate lower than
> >> the wire since the velocity is less than the speed of light.
> >>
> >> Why then, do long space wound coils resonate at a frequency higher
> >> than expected? This has nothing to do with the LC ratio either. I would
> >> expect that no matter what gain or reduction of L vs C for a given
> >> geometry, they should always result in a frequecy lower than that of
> >> a straight wire. Whats going on here???
> >>
> >> Before I go and re-invent the wheel, does anyone have an explaination
> >> and/or experimental data on this?
> >>
> >> Curious in NY
> >> Jim McVey
> >
> >Assume one has a 1/4 wave length of wire straightened out as an aerial
> >(1/4 wave monopole). It has a particular distributed L and C. Now
> >coil that wire up. C drops and L rises through mutual inductance
> >between the turns. However, M between turns is less than 1 and Cdistr
> >is dependent on wire/coil length. The only reasonable explanation I
> >have been able to come up with is that due to the less than M=1
> >between turns, C drops faster than L rises when the wire is coiled up
> >in this way. Hence Fr is higher than for the straight wire.
> >
> >Malcolm
> >
> >