John Ferrell wrote in
news

Now to digest them and try a Lab project or two...
John Ferrell W8CCW

The challenge is to read the material and lose the stuff that is just
plain wrong. When you find content that is wrong, it damages the
credibility of the whole paper.

To demonstrate how poorly common mode current is understand, the
following is a quote from MFJ's web site page describing their MFJ-835
twin needle "RF IN-LINE CURRENT METER, BAL.LINE, 1-30MHZ, 3AMP":

"How do you detect imbalance in open-wire or ladder line? By measuring
and comparing each feedline wire current -- your feedline is balanced if
the currents are equal."

Well, the line is balanced if the currents are equal in magnitude and
opposite in phase (ie 180° out of phase). The MFJ-835 compares ONLY the
magnitude, and it is true that if there is zero common mode current, a
properly calibrated MFJ-835 will indicate balance, but it is NOT true
that if the MFJ-835 indicates balance (equal magnitudes) that there is
necessarily zero common mode current.

You will find articles on the net where authors have expounded the
perfection of their station using the MFJ-835 as proof of zero common
mode current, some even explaining how they continuously monitor balance
(apparently at a fixed point in the line). The instrument is not suited
to the job, and their results are flawed. The articles would make a good
read if they weren't flawed.

Owen