A balun is a device that connects a balanced line to an unbalanced line. It allows a signal of one impedance value to be transmitted over a cable that uses a different impedance. Impedance is simply a measure of opposition to alternating current. A video balun allows a user to send video signals over a cable not meant for video. A common situation involving video baluns is for them to be used with Cat5 cable. Coax cable, which transmits video, has an impedance of 75 ohm while Cat5 has a 100 ohm impedance. Baluns, therefore, convert the original impedance to the impedance of the cable and then back. Baluns are used in pairs; you need one on each end of the cable. Transmitting video over Cat5 without the use of video baluns will produce a picture with ghosting as delays in the signal will occur.
The word balun is derived from the words BALance and UNbalance, as the device takes a signal from a balanced line, converts it to a signal for use in an unbalanced line, and vice versa. A balanced line has two conductors and is one in which the current is equal in opposite directions while an unbalanced line has just one conductor with current returning via a common ground. The reason for using a balun is because Cat5 cable costs less then coax cable. Another factor is ease of installation. The quality of video is also excellent when using Cat5 cable. Cat5 provides for excellent balance, meaning the video signal will not be affected by other signals. Most of the electrical noise and RF interference which affect coaxial cables are eliminated.
Types of Baluns
There are two types of baluns: active and passive. Active baluns use amplification to push the signal further than can be sent using a passive balun. As such, they require a 12 volt DC power source. A video signal can be transmitted an average of 5000 feet with Cat5 cable and an active balun. Active baluns can even send data and low voltage power. The average transmission range of a passive balun is 2000 feet when using Cat5 cable. A Cyrex CBLNT passive balun with a coax tail