Balanced and unbalanced loads:

A balanced load is that whose terminals can be reversed without significantly affecting the circuit behavior. A plain resistor is a good example of it. The two wire antenna input in the television receiver is another example of the balanced load. A balanced transmission line is generally a two wire line, like television antenna ribbon.

An unbalanced load is a load that should be connected some specific way; switching its leads will result in improper circuit operation. Some radio antennas are of this particular type. Generally, unbalanced sources and loads have one side which is connected to ground. The coaxial input of the television receiver can be unbalanced; the shield of the cable is grounded. An unbalanced transmission line is a coaxial line, such as you find in the cable television system.

Normally, you cannot connect the unbalanced line to balanced load, or balanced line to an unbalanced load, and expect good performance from an electrical or electronic system. But the transformer can allow for mating between these 2 types of systems.

In the Figure given below, a balanced to unbalanced transformer is shown. Note that balanced side is center tapped, and the tap is grounded. In the Figure B, an unbalanced to balanced transformer is explained. Again, balanced side has a grounded center tap.

Figure--   At point  A, a balanced to unbalanced  transformer. At point B, an unbalanced to balanced transformer.

The turns ratio of a balanced to unbalanced or unbalanced to balanced transformer might be 1:1, but it does not have to be. If the impedances of the balanced and unbalanced parts of systems are same, then a 1:1 turns ratio is ideal or perfect. But if the impedances differ, the turns ratio should be such that both the impedances are matched.