Re: Tesla Notes Re: 1/4 wave theory/cite the variance?

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I think the 1/4 wave thing, in re Tesla coils, is not so much the 1/4 ground
plane antenna, but the quarter wavelength long transmission line
transformer.  (a "resonant transformer", for those so inclined)  For such a
line Z0^2 = Z1*Z2, where Z0 is the characteristic impedance of the
transmission line, and Z1 and Z2 are the impedances at the two ends.    If
you drive a very low impedance on one end, that makes the opposite end a
very high impedance.  Low impedance = high current, low voltage; high
impedance = low current, high voltage ( E = Z * I, after all)

Consider, for a moment, a 1/4 wave line of characteristic impedance 300
ohms.  Imagine you are driving it with something of impedance, say 1 ohm, at
1 volt (1 amp, 1 watt). At the other end of the line, the impedance will be
300*300 or 90,000.  Same power, so it will be 90,000 volts and 1/90,000 amp.
Now consider a transmission line with a characteristic impedance of say,
10,000 ohms.  Same quarter wave.. Now, the transformer ratio is
100,000,000...  Think about what a 10K ohm transmission line would need to
be.. Lots of inductance (like a long solenoid...) distributed along the
line.  How about a long skinny secondary?  Long skinny secondary with a
helical primary at one end, tiny topload... Most of the power is being
coupled in at the end... It starts to look more and more like a transmission
line transformer (and like the popular designs of 30 years ago or so... long
skinny coils, zillions of turns, helical primary...small topload)...

For those of you with moderately high powered HF sources (say 50-100 watts)
you can make an interesting demonstration using a pair of bare wires spaced
to make a transmission line (copper tubing works well).  If you've got a
10meter transmitter (around 28 MHz), a (free space) quarter wavelength will
be 2.5 meters (about 8 feet).  Short one end of the transmission line,
couple the transmitter to it using a few turns and a suitable toroid (so
that the 50 ohms out of the transmitter is transformed to a few ohms).  Fire
up the transmitter, and you can watch the corona/spark form at the 1/4 wave
point, and you can move it around by changing frequency.  A fine
demonstration of VSWR, by the way...  You can get the transmitter match
better by moving the ferrite toroid along one conductor a bit from the short
(which is zero ohms, and you want to find a place where the impedance is a
bit higher).



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, February 18, 2002 12:37 AM
Subject: Tesla Notes Re: 1/4 wave theory/cite the variance?


> Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<davep-at-quik-dot-com>
>
> (Related, to save a post:
> Yes, i understand 1/4 wave is 1/4 wave over ground, which acts like a
> 1/2 wave...  etc...  One level deeper than seems needful here.
>
>
> Tesla list wrote:
>
> > I should point out that much of the 1/4 wave "myth" comes from the
Colorado
> > Springs Notes as do a fair number of other "myths" about Tesla coils.
>
> > The Colorado springs notes are Tesla's personal notes he took at the
time.
> > He NEVER intended for someone to find it 80 years later and publish it
and
> > send tens of thousands copies all over the world to hungry Tesla coil
> > builders.  If he had, he would have removed all the mistakes.
>
> Respectfully submit that other views on this are held.
> I suggest that this is apropos to the extent that those notes
> DO describe a working coilers lab.
> Students of Tesla have stated that:
> He wrote the notes specifically BECAUSE lack of
> notes had hurt him in patent disputes in the past.
>
> Taking this as accurate (i think it was Marc Siefer????)
> Then one may infer that the notes ARE intended as accurate.
>
> > Tesla used the 1/4 wave thing a lot in his calculations "there" because
> > that is all he had "at that time".  Much of the notes are filled with
Tesla
> > struggling with the fact that "it didn't work".  Later on, Tesla
certainly
> > understood the problems with his old calcualtions back then.  However,
If
> > you read the notes, they do sound like Tesla had it all figured out,
> > "before he tested it"!
>
> As someone who has had to keep a lab book, I read the notes
> (as to lab procedure, skipping various side notes) as someone
> doing cut and try.  Start with an idea, extend it until it
> won't extend, then try to find a way around.
>
> > So be very careful of getting "facts" from the Colorado Springs notes.
The
> > experiments are wonderful but the "analysis" was not ready for prime
time.
> > I hate to hear people argue that soemthing there is the truth when Tesla
> > himself would not defended it in light of his later understanding.
>
> > For fun, if one has any old Tesla notes form 20 years ago.  Imagine how
> > they would sound "now" if they suddenly made the six o'clock news!
> > Maybe I should go burn mine :o))
>
> I suggest that there is an element (tho i disagree somewhat)
> in Dave Ts point that Tesla's coils WERE space wound, reducing,
> if not eliminating capacitance effects.  Also, Tesla's Colorado
> Springs coils were HUGE in diameter and SHORT in height.  This
> is the end of the aspect ration range where the wire length for
> a 1/4 wave (over ground, resonating as a half wave, counting
> the image....   8)))  DOES approach a 1/4 wave in physical
> length.
>
> Few since have had the luxury of working on such a scale.
> (Anyone have parameters handy for Robert Golka's coil?).
>
> best
> dwp
>
>
>