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Re: Bang the rocks together harder lumpophiles
Hi Antonio,
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: 20 April 2000 04:49
Subject: Re: Bang the rocks together harder lumpophiles
>Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
>
>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 experiments
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.
It would not be the first time I have done that but not this time.
>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.
I am sorry to be blunt but this is not correct the impedance of a
losseless transmission line is resistive, hence for a PROPAGATING
wave the voltage is ALWAYS in phase with the current.
Your mechanical analogue appears odd, V x I = power, position x speed=?
V x dV/dt=? I would expect force x velocity = power
>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.
I dont think I understood the above paragraphs. If the line is not
resonating
the in to out phase could be anything it depends on the length of line. At
resonance what is being measured is the phase of a standing wave with
respect
to the input. A standing wave is just that it does not move. Its the sum of
a forward and backward travelling. It has constant phase it only
changes in amplitude. Its phase is pinned to the reflection at the end of
the line
that created it. If you could remove the standing wave you would be able to
observe the progressive phase change of the input signal.
At resonance the input current is in phase with the input voltage thats one
definition of resonance. ( assuming resistive drive). If the were no losses
the input voltage would be zero ie it would look like a short.
I suspect you are talking about the relative phase of the current and
voltage in a standing wave which is 90deg.
I think there has been a lot of confusion about standing wave and
propagating
waves. This is what produced the "no phase shift so its not a transmission
line" view.
In effect the two types of waves are spatial and temporal.
One moves in space and one moves in time.
The difficulty is that if you put a scope probe on either one you get the
same sinewave hence confusion. At first it fooled me too.
It may be possible to have a internally consistent theory of how the coil
works
using standing waves with particular properties. I prefer the main stream or
traditional theory of forward and backward travelling waves.
I missed the posting of your model I will look for it.
Regards Bob