[TowerTalk] To get a truly balanced antenna feed

[Paul Christensen]

>"Moving on to "How might you measure CM current or line balance?" I'm
afraid the two-ammeters method is only the roughest of checks. Because it
only measures the overall magnitudes of the currents in the two legs, it is
only capable of detecting gross levels of unbalance. A more accurate
measurement must also take account of the differing phases in the two legs.
The simplest method would indeed be to pass the line through a large toroid,
and extract a sample of CM signal on a terminated secondary winding."

Ian,

http://www.wz5q.net/index/shack_data/tuna.htm

Have a look at WZ5Q's work where he monitors both line current and phase
with toroidal sample loops (scroll to the bottom of the page).  Note that he
takes scope phase measurements directly at the tuner output.  Measurements
made at a point further along the line may yield a different result if
there's unintentional line coupling to close objects.    Still, it shows an
awareness of the line balance performance issue. 

Paul, W9AC