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Re: Bang the rocks together harder lumpophiles

Hi Bob,

At 01:36 PM 04/16/2000 -0400, you wrote:
snip...
>
>I assume your coax experiment is an attempt to disprove my assertion that
>there is zero phase in a standing wave by constructing 1/4 resonator with
>the coax and performing a test. OK

Antonio did this very test and he got to output 90 degrees out of phase
with the input.

>You dont have the correct set up. You have
>the driven end terminated in 100ohm. Thats more like an open circuit than a
>short. Connect say a 4.7ohm or 1ohm resistor across the input and make sure
>YOU HAVE A 1/4 WAVELENGTH.  Cut the cable in half and reconnect it so you
>have access to the central conductor. Repeat the experiment and check the
>phase at the junction. It will be inphase with the end just a lower
>amplitude.  Half way down the cable the forward wave will lead the end
>by 45deg and the reflected signal will lag by 45deg.the sum is zero.  In
>fact the phase will be zero where ever you cut the coax except at the 
>driven end.  Just like your ruler
>or a Tesla coil.

You bring up an interesting point about the input impedance.  Since we
clamp "Malcolm's ruler" in a vice, we should also drive the coil with a
very low input impedance.  More easily said than done since the system then
has a very high Q.

MicroSim can do your test easily and I ran the situation with the results here:

http://users.better-dot-org/tfritz/site/misc/Bob01.gif

MicroSim confirms your experiment and I trust MicroSim. ;-)  You have
brought up a very interesting twist to all this!

>
>Lets focus our attention on the main object of our interest the secondary
>coil. You suggest the analogy of a vibrating clamped steel ruler. I agree
>but this is a almost perfect example of a 1/4 wave resonator. Its shorted at
>one end by the clamp.  The other end is free to move that's an open circuit.
>It also has a finite propagation time for transfers waves . The vibration
>you see is a standing wave resulting from the superposition of the forward
>and backward travelling waves propagating along ruler.  As you correctly
>pointed out no apparent phase shift only a quarter of a sine wave changing
>in amplitude.
>
>Hopefully you cut your coax so you know you can't to measure the propagation
>delay from the phase shift. measurements in your coil when its resonating.
>So you must remove the reflection or use a low frequency square
>wave as I previously suggested .  I now think (a minor conversion for me)
>that the coil is significantly dispersive (different frequencies travel at
>different velocities) so this could complicated the interpretation of an
>experiment using square waves.  So stick to sine waves and  you want
>have to worry so much  about terminating the generator and other things and
>hopefully the result may be more convincing.

Ken and I were playing with sine waves just at the instant of turn one.  A
lumped system and a transmission line system do have variation here, but
the probe loading is messing with our results at the moment.  I looked at
your taped line model at the instant of turn on and got the following:

http://users.better-dot-org/tfritz/site/misc/Bob02.gif

>
>So what you must do is terminating the coil in its characteristic impedance
>at both ends.
>I have tried to think off a quick  and foolproof (well you screwed up the
>coax test) way of you doing this but have not come up with one.

I trust MicroSim.  It's hard to screw up and I can probe points without
loading anything.  But I think I am now convinced anyway that the phase
along the coax is consist ant once the resonance has built up.  I think the
key is to look at the first "impulse" or "step response of a real coil and
measure the time it takes for the stimulus to reach to top of the coil.
Lumped and T-line systems seem to vary greatly in that respect.

>
>The best I can do is as follows.  

I will have to study your test more and get it set up, but I wanted to get
these first things out of the way here.  Thanks for your ideas on all this!
 Sooner or latter, we all should be able to get to the bottom of all this!

Cheers,

	Terry