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?
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.
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.