This Separator/Combiner is used to convert 75 Ohm connections into 300 Ohm connections. It is often used on old VCR's and TV's with F inputs and it is converted to external antennas. This allows you to run your signal longer distances without losing quality.
A: A balun is a small transformer which converts an audio or video signal from unbalanced to balanced and vice versa (hence the term 'bal*un'). By doing so baluns make the necessary impedance adjustment for audio-visual signal transmission between different wiring systems