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Another obnoxious lumped theory supporting post ;-))

Hi All,

	Inspired by Ken and Robert I did an interesting experiment.  I measured
the top and bottom phase shift of a coax cable at 1/4 wave open load
resonance and a secondary coil top and bottom at open load resonance.

The coax is just 100 feet of RG-8 TV cable driven from a sine generator.  I
grounded the negative terminal of the generator (It can normally float) and
ran the output through a 100 ohm resistor to the coil.  The generator has a
one ohm output but the load at resonance draws too much current from it, so
I need a resistor.  I then placed a scope probe next to the wire from the
generator feeding the coax to capacitively couple the voltage (it has a
short wire on it).  This picks up the input voltage.  I put a short wire on
the other end of the coax next to the other scope probe to pick up the
output voltage.  I had the sensitivity on the scope turned way up and I was
able to get a good signal off both probes.

A picture of the cable and probes is here:
http://users.better-dot-org/tfritz/site/misc/quarter/Image2.jpg

I then adjusted the generator to get resonance.  It was a little tricky
since the cable seems to like harmonics and the input signal level was not
great but I think it was right.  

The scope picture is here:
http://users.better-dot-org/tfritz/site/misc/quarter/Image1.jpg

Notice how the phase at the open end (top) is 90 degrees later than the
phase at the generator end (bottom).  See, that transmission line stuff
really does work for transmission lines! ;-))

I then disconnected the coax and hooked the generator to the base of a
secondary (1180 turns #24 3.25 Dia. 26.125 long).  The same scope probe was
laid next the input wire just like before with the coax as shown:

http://users.better-dot-org/tfritz/site/misc/quarter/Image5.jpg

The other probe was laid on the top of the coil as shown:

http://users.better-dot-org/tfritz/site/misc/quarter/Image4.jpg

I adjusted the generator to get resonance (first harmonic) as usual and
snapped the scope picture:

http://users.better-dot-org/tfritz/site/misc/quarter/Image3.jpg

Geee.  Is not zero.  Maybe 5 degrees off.  I'm still not getting a warm
fuzzy about all this transmission line stuff! ;-))  I moved the probes
around and all that looking for the nice 90 degree phase shift to coax had
but I just can't find it.

The 3F0 harmonic was there in all it's glory at -180 degrees and the 5Fo
was back at zero degrees again.  Another thing to try is to put one probe
monitoring the top of the coil and take the other probe and move it along
the coil (you will have to retune).  That 90 degrees phase shift was not
there.  The coax worked just as it should.

So electricity really does have to run the length of the 100 feet of coax
and the velocity factor stuff about coax cable is true.  The wave really
does take 1/4wave to get to the other end and the phase shift is 90 degrees
just like it should be.  But in a repeating the test as closely as possible
with a secondary coil, the 90 degree phase shift was not there.

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...

I point to Malcolm's example of taking a steel ruler and clamping one end
in a vice and thumping the top end to get it oscillating.  Hardly any phase
shift in that situation and I think he is right in that all the mechanisms
there are analogous to or Tesla coils.

In a transmission line, you have inductance and capacitance per length that
slows the wave propagation some.  But you really need pure wire length to
do the majority of the wave delay and phase shifting.  You can take a very
short line and come up with super high values of inductance and capacitance
per length to get that slow wave (the key behind delay lines) but those
values are simply not real life.  Once the wire length aspect of Tesla coil
theory fell apart, the 1/4 wave transmission line theories were doomed too.
 You have lots if inductance for your RLGC values but there just isn't
enough capacitance to slow the darn wave down to get a 90 degree shift (5
degrees, yes).  You can make up an imaginary number to get there but unless
you pack barium titanate around your coil, that is not realistic.

No doubt that the secondary self capacitance is "distributed".  However,
the caps in my MMC are rather "distributed" too and they don't cause phase
shift. They are far closer to each other than the coil's wavelength.  by
the same argument, I would submit that the top and bottom of a secondary
coil are also far shorted than the wavelength despite the distributed
capacitance...

Whew!  Terry's giving the 1/4 wave guys a rough time!  :-))

Ok, their turn...

Cheers,

	Terry