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Re: Bang the rocks together harder lumpophiles
Tesla List wrote:
>
> Original Poster: "Robert Jones" <alwynj48-at-earthlink-dot-net>
> But I am totally perplexed as to why with so many examples of standing waves
> with no phase shift that its difficult for so many to accept its true for a
> Tesla coil and presumable most on the list are engineers or at least the
> ones with scopes and things. You must have done those experiments at school
> with the lycopodium powder and tubes what about the string expeiments with
> bits of paper. Can somebody explain it. What's special about a Tesla coil.
> I am starting to feel its a religious believe and I am a heretic. Just do
> the propagation measurement with a matched terminated coil as I have
> described.
You are probably mixing the phase relationships between current
x voltage at some point in the line and current x current or
voltage x voltage at different points of the line.
A lossless transmission line, or a lossless coil, is a purely reactive
element, and so, in sinusoidal steady state conditions (CW), all
voltages
are at +/-90 degrees with all currents. In the mechanical analogs,
this would be the relation between positions and speeds.
For the same reason, the phase relationship between voltages at
different points and currents at different points is always 0 or 180
degrees. This is easy to observe in the mechanical analogs too.
The insertion of small losses (resistance) at some points, causes
the appearance of voltage x voltage and current x current
phase relationships at 90 degrees, at the points and frequencies
where the transitions between 0 and 180 degrees would occur.
At all these points, one of the voltages or currents is much smaller
that the other (in the lossless case one would be 0 or infinite),
and what you are measuring is effectively the phase relationship
between current and phase in the lossless section, at +/- 90
degrees. This is easy to observe in a resonating string too, where
the nodal points become less defined.
The typical example is the one being mostly discussed here:
A low-impedance voltage source is connected to one side of
the line/coil and the voltage at the other side is measured.
What is observed is that for most frequencies the phase
relationship between input and output voltages is around
0 or 180 degrees, with input and output voltages of similar
magnitudes. At the resonances, the output voltage increases,
and a +/-90 degrees phase relationship between input and
output voltages appears. A model that I posted some days ago
shows clearly why. What is being measured is effectively
the relation between the output voltage and the input
current.
Antonio Carlos M. de Queiroz