[TowerTalk] To get a truly balanced antenna feed

[Paul Christensen]

>"That is why, out of the many thousands of amateurs who claim to be using "balanced feedline", there are few or none who can actually *prove* it. All the rest are really just expressing a hope or a wish which will almost never be granted."

Positively depressing, Ian.  If we can achieve reasonable, albeit not perfect line balance, does it really matter?  Consider a wire dipole strung between two tall trees and fed with open wire line straight down to a symmetrical, balanced ATU (e.g., link-coupled) installed just above ground level.  If thermocouple ammeters placed on each line at the tuner 's output report equal current, then it's reasonable to assume that line current is well balanced.  But this also assumes the line is located in the clear and not coupling to nearby objects.  My home QTH closely follows this description, although the link-coupled tuner is replaced with a motorized, switched-symmetrical L type with CM choke at the coaxial input.

Sure, that's a near ideal set-up and probably to your point, the typical installation consists of a non-symmetrical tuner on the operating desktop, feeding window line that meanders through the  house, along walls, in the attic, near metallic gutters, etc.  

Although difficult to manage, one could place ammeters or shunted pilot lamps at equal distances from the feed-point on the dipole itself, and observe current.  Some of the first experiments using this method were developed during the 1920s and covered in QST.   In the early literature, transposition blocks spaced at regular intervals along the line were used with the intent to force the line into balance.  By the 1940s these devices seemed to have disappeared, possibly because of the availability and easy installation of coaxial lines after the war.   

Paul, W9AC