Cecil Moore wrote:
Richard Clark wrote:

Cecil Moore wrote:

The referenced W8JI 3 nS "measurement" was the delay
in a 2' dia, 100 T, 10" long loading coil on 4 MHz,
i.e. 4.5 degrees.


Jim's point is that it can be done!


In that particular coil at 4 MHz - no, it cannot be done.

measuring the phase shift between two sinusoidal currents at 4MHz to a
precision of hundredths of a degree is easy. HP sold a box (the 8405
vector voltmeter) that did this decades ago. Actually, they've sold two
different boxes (the 8508A ), both of which I've used. My point was
that you don't even need to go that far, and that most experimentally
oriented hams probably have stuff that can be used to make an improvised
measurement of that accuracy.

I note that the TAPR or N2PK VNAs could easily do the measurement.

The practical challenge is figuring out how to get a current probe that
doesn't perturb the measurement. Optical pickups are one approach. high
impedance probes with resistive leads are another. Both are commonly
used in antenna measurements where you want to measure the fields directly.

One could, of course, also do a near field range type measurement, but
the inversion from measurements at one set of locations to values at
another presumes that you believe Maxwell's equations, which I seem to
think might be at issue among the contenders here.


now, if you said you wanted to measure tenths of a degree at 50 GHz, I'd
say you have a real challenge in front of you