Walter Maxwell, W2DU listed an enviable collection of impedance
measuring devices. He`s prepared. Walter also wrote:
"In my impedance-measuring arsenal is the Wayne Kerr B108 admittance
bridge. The beautiful aspect of this bridge is that its unknown
terminals are balanced, thus allowing direct measurement of balanced
lines."

Yes. Balanced unknown terminals are convenient for a commercial
shortwave operator located away from the seashore. Horizontal wave
polarization with balanced feedlines is economical as compared with coax
for high power.

Unbalanced vertical antennas are convenient for groundwaves to extend
beyond the horizon for the mediumwave broadcaster. These antennas are
conveniently fed by coax of the concentric pipe or skeletal types. All
groundwaves are vertically polarized. These can travel very far at low
and medium frequencies. Attenuation of high frequency groundwaves is
severe. There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.

Bottom line is that shortwave broadcasters transmit from horizontal
antennas and mediumwave broadcasters transmit from vertical antennas.
For shortwave, the target is reached via the ionosphere. For mediumwave,
the target is reached via the earth`s surface which is involved in
reaching beyond the line of sight.

For a dipole, you are likely to prefer a balanced bridge. For a
monopole, you are likely to prefer an unbalanced bridge.

Best regards, Richard Harrison, KB5WZI