It sounds like the predictions are in. Among the several people who
believe that the current out of a small inductor doesn't equal the
current in, only Yuri was able to calculate a predicted value for the
test, of 2.5 - 5% reduction in current at the output compared to the
input, with a phase shift of about 18 degrees.

What I measured was a 3.1% reduction in magnitude from input to output,
with no discernible phase shift. The 3.1% is an average of two readings,
with the input and output probes exchanged. The output was smaller than
the input in both measurements, about 2% and 4%. So I believe there's a
real difference between output and input current, although with the
accuracy of my measurements, I only have reasonable confidence it's
somewhere between 1 and 5%. I can resolve about 2-3 degrees of phase
shift, though, and I couldn't discern any at all. (Yes, the scope
trigger was from one channel, not alternating.) So I have very high
confidence that Yuri's prediction of 18 degrees is incorrect.

I don't subscribe to the notion that the current out of a very small
inductor should be different than the current in due to some magical
property it acquires when connected to an antenna. My working hypothesis
is that the currrent difference I did see was due to stray capacitance,
either from the probes or simply to the Earth and other objects. It
would take an equivalent of 6.8 pF at the output of the coil (that is,
between the coil output and the current probe) to get 3% reduction, and
only about 1/3 that amount to see the minimum value of reduction of 1% I
estimate was actually present.

I repeated the test on the bench, with a 36 ohm resistor in series with
a 220 pF capacitor substituting for the antenna. The result was a 2.3%
output:input reduction, again with no discernible phase shift. This is
within the measurement error of being the same result. This is what
should be expected -- except for unintentional coupling to the antenna's
field, the inductor's environment is the same on the bench as at the
antenna base, in these single frequency, steady state tests. (That also
contradicts what some newsgroup participants have been claiming.)

So, although the small output:input current reduction was within Yuri's
prediction, the phase shift certainly wasn't. If time permits, I'll make
a more idealized antenna and repeat the measurements with a larger
inductor at the base of a more reactive antenna. I'll predict in advance
that if I double the amount of loading L, I'll approximately double the
amount of current magnitude attenuation -- that is, to somewhere around
6%. That's what should be expected if the cause of the attenuation is
stray C or a similar phenomenon.

I've added a picture to the
http://eznec.com/rraa/Inductor_Current_Measurement.html page, showing
the overall setup including the scope. It gives a little better
perspective on the relative sizes of various objects.

Roy Lewallen, W7EL