dykesc wrote:
First thanks for the many replies to posts I make here. I enjoy the
dialogue and am fortunate to have access to the knowledge and
experience here.

Other than my MFJ-259B and my DMM, the only other piece of test
equipment I have is an oscilloscope. Would it be possible to wrap
several turns of light gauge enameled wire around the jacket of the
coax at my operating position, attach the oscope probes and detect and
possibly measure the amplitude of any common mode currents?


That will work, but here's a way to make an actual quantitative
measurement, assuming the bandwidth of your 'scope is at least a few
times the highest frequency you want to measu

1. Find a ferrite core large enough to fit over the coax and connector.
Common type 43 is fine, or any of the lower frequency ferrites (e.g.,
Fair-Rite/Amidon 70 series) if you're measuring at HF.
2. Wind 10 turns (10 passes through the core) of enameled wire on the
core. Connect a 100 ohm resistor across the winding with leads as short
as possible.
3. Slide the core over the coax. Measure the voltage across the resistor
with the 'scope. The common mode current in amperes = 10 * the 'scope
voltage(*).

(*) The current through the resistor is 1/10 the common mode current due
to the 1:10 turns ratio. The voltage across the resistor is i * R = 1/10
the common mode current * 100 = 10 * the common mode current. The
transformer will look like a one ohm series resistance (R / N^2, where N
is the turns ratio of 10) to the common mode current.

Roy Lewallen, W7EL