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Re: Another obnoxious lumped theory supporting post ;-))
Tesla List wrote:
>
> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>...
> So give it a try and tell me what's wrong. I think if I did all that RGLC
> transmission line stuff I could explain the 5 degree phase shift (as I have
> before) but there really isn't much that can go wrong with this test and I
> invite anyone to give it a try...
Today I tried also to see what happens with a transmission line, but I
connected a long coaxial cable directly to both channels of an
oscilloscope,
with one channel connected also to a RF signal generator. The results
were as expected. Periodical notches at the input, and at each of them
the output signal was at 90 degrees with the output signal.
The same must happen with a long coil without top load. At all the
resonances the output is at 90 degrees with the input.
Check your experimental setup.
Even the lumped model predicts this:
--->Il
o----Rg-----R-----L-----+
+ + + | +
Vin V1 Vlc C V2
- - - | -
o-----------------------+
Vin is the signal generator. Rg the resistance in series with it. L and
C are the lumped model for the coil. R is the equivalent series
resistance
of the coil, conveniently moved to the input.
Let Vin=A*cos(w*t)
At resonance, the ideal voltage Vlc=0
The measured input voltage is then V1=A*R/(Rg+R)*cos(w*t)
The current in the coil is Il=A/(Rg+R)*cos(w*t)
And the obtained output voltage is V2=-L*dIl/dt=A*w*L/(Rg+R)*sin(w*t),
Or V2=A*Q*sin(w*t). Amplified by "Q" and delayed 90 degrees.
The same would happen with any reactive circuit in place of the LC
circuit, in CW (steady state) conditions. Note that you are affectively
measuring the phase relationship between current and voltage in the
reactive circuit. The phase difference must be 90 degrees, or energy
would be entering or leaving the reactive portion.
Antonio Carlos M. de Queiroz