Re: Series resonance/Was: Waveguide TC

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>



>  > Original poster: "Jolyon Vater Cox by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

>  > Jim,
>  > From what I understand an open-ended 1/4 wave transmission

>>line is series-resonant circuit; series resonant tuned

>>circuit have 90 degree phase shift between current at
>  > the driven end (low impedance) and current at the terminal

>>end (high impedance).
>Except that by Kirchoffs Current Law, the current in and out

>of the terminals must sum to zero.

         My recollection is that Kirchoffs law applies to
         _circuits.  Closed entities, or things in them.
         By observation:
                 Antenna circuits need not be closed (some are).
                 1/4 wave antennas DO have a current peak at the
                 base.
         (other 'series resonant' circuits may not....)

>Therefore the current at the bottom of the secondary has to

>be equal to the current at the top of the secondary.

         cf above.
         Also:
         Behaviour of Tesla Secondaries, in this regard, likely
         changes with MODE:
                 When sparking, the top terminal is not open
                 and the resonance may not be strong.

                 When NOT sparking, i suggest the resonance is
                 stronger.
         (Tesla, apparently, planned to operate in the second
         mode.  (I'm not convinced he'd have got much done,
         but that is Another discussion, for another forum.)

>EXCEPT.. there is some parasitic capacitance (not insignificant) from the
>secondary winding to "ground", and some current flows through that
>capacitance.  But, a number of folks have made measurements of the current
>at top and bottom and find they are only a few degrees apart.
         Sparking or not?



>  > A lumped series-resonant circuit can be visualised as an inductor L and a
>  > capacitor C
>  > in series with a signal source or "generator". Surely there is a 90 degree
>  > phase shift between current at the driven end and the current at the
>  > "terminal" end i.e. current flowing "through" the capacitor?

>Nope.. in a series circuit, the currents all have to be equal.

         In a closed series circuit...
         And the use of 'series resonance' in this case is
         a mental model, an analogy, and need not be pushed too
         far.

>The 90 degree phase shift is between the voltage across the

>device and the current through the device.
         The measurements on 1/4 wave antennas differ.

         (Whether this has direct relevance to sparking Tesla
         coils is a seperate matter...


>  > There is a common belief (incorrect?) that the secondary of a TC is a
>  > series-resonant
>  > circuit - I might be wrong but would this not presume a 90 degree phase
>  > shift between input and output-
>  > whereas observations made on real TCs suggest little or no phase shift
>  > between currents at the grounded and the terminal ends.

>Indeed the secondary of a TC IS a series resonant LC circuit. Actually, a
>bit more complex, the TC is a pair of coupled series resonant circuits,
>coupled via the flux linked between secondary and primary.

>  > Is the "series-resonant secondary" like the quarterwave resonant theory
>  > incorrect
>  > -or is it possible to have a series-resonant tuned circuit with
>  > little or NO phase shift between low-impedance input and high-impedance
>  > output?

>  > Or does the series-resonant voltage boosting effect involve not just the
>  > secondary but
>  > the primary as well -with the primary leakage inductance resonating with a
>  > "transformed" value of the secondary capacitance via the magnetic
>coupling?


>In a "disruptive" TC (i.e. not a CW oscillator), there's no "boosting" due
>to resonance (perhaps you're thinking of the voltage rise due to resonance
>in a tuned circuit?), because you're only putting in one "lump" of energy,
>rather than a new burst on every cycle (as in a CW coil, where resonant rise
>IS the mechanism, or, in a transmission line transformer, which is an
>inherently narrow band device).

-- 
         best
         dwp

...the net of a million lies...
         Vernor Vinge
There are Many Web Sites which Say Many Things.
         -me