On Dec 7, 5:09 pm, Cecil Moore wrote:
This is a request to any readers of r.r.a.a who are
capable of performing the experiment that I performed.

Use the EXCEL file at:

http://www.w5dxp.com/CoilZ0VF.xls

to estimate the Z0 of your test coil. If the test entry
is greater than 1.0, try another coil.

Here is the test setup using a 75m Texas Bugcatcher coil:

http://www.w5dxp.com/coiltest.gif

Using a 50 ohm source, install an autotransformer to
achieve the Z0 of the test coil on its output.

Load the test coil with a non-inductive resistance
equal to its Z0 value.

This will ensure that most of the current flowing
through the coil is traveling-wave current and not
standing-wave current.

Report the phase shift through the test coil.

This is an easy test to do. Of course, none of the
resident gurus will run the test or report the results
if they do run the test because it will prove their
old wives' tale to be wrong.

This experiment presents some challenges, particularly
the need for current probes, but I have some questions
on the physical arrangement of test circuit.

You appear to think of the coil as a section of transmission
line, having assigned it a Z0 of 4kohm. But a transmission
line has two terminals at each end. I only find one at each
end here. How is it that this exhibits transmission line
behaviour?

The auto transformer would appear to be unnecessary
since any reflections at the source end will simply add
to the forward signal which will appear at the output
and therefore compensate perfectly when comparing
the input and the output. Proper termination of the
output is necessary because reflections there may
alter the measurements. Leaving out the transformer
would simplify the experient. Do we really need it?

The circuit layout seems to just have a wire from
the bottom of the resistor back to the source. This is
only appropriate if you are assuming that all
components can be treated as lumped (and the
wire ignored) at the frequencies and component
size of interest. But I thought your main argument
was that these components were sufficiently large
that they could not be treated as lumped. If this
is the case, then the routing of the return wire
will have significant effects on the result. How
did you route this wire?

If the coil can be treated as a transmission line,
then the delay can be measured by simply sampling
the voltage at the input and the output. This will
be a much easier experiment than measuring the
current. Should I expect the same results if
I measure the voltage?

....Keith