Definition
A transmission line in which one of the two conductors is held at ground potential while the other carries the signal. Coaxial cable is the most common example: the inner conductor carries the signal, and the outer braided shield is grounded. The two conductors do not carry equal and opposite voltages with respect to ground, which is what makes the line 'unbalanced.'
Plain English
A signal-carrying cable where one wire does the work and the other is tied to ground. Coax cable is the everyday example. The two sides aren't electrically equal to ground, which is where the name comes from.
Context Anchor
Seen in aircraft radio and antenna installation or troubleshooting, especially when describing the cable between a radio and its antenna.
Derivation
Unbalanced' here describes the electrical relationship of the two conductors to ground, not physical balance. One conductor is grounded, the other isn't, so the line is electrically lopsided with respect to ground.
Why Pilots Care
Proper use prevents signal loss, interference, and poor radio performance in aircraft communications and navigation systems.
Intuition Check
Unbalanced does not mean the cable is physically uneven or unsafe by itself. Here it means one electrical side is tied to ground or shielding while the other side carries the signal.
Example Sentence 1
The VHF radio antenna is fed by an unbalanced transmission line, with the coax shield grounded to the airframe.
Example Sentence 2
Technicians checked the unbalanced transmission line after noticing weak transponder returns on the test set.