View of the baluns

View of the packaging

The set is designed to transmit video signal from a single source using a twisted-pair cable. Each of the video transformers (baluns) has a flexible cable terminated with BNC connector, which ensures easy connection even to closely spaced BNC sockets.
One of the devices matches the 75 ohm impedance of the unbalanced source to the impedance of the balanced line usually formed by a pair of UTP cable, the second performs the opposite function. The video signal can be transmitted over a distance up to 400 m (UTP CAT5e).

The installer should pay attention to connecting the appropriate wires to the correct terminals: (+) to (+) and (-) to (-). Improper connection will cause interference.

CMRR in video transformers (baluns). "Balun" is the short for "Balance-Unbalance", in CCTV applications meaning a transformer for changing the transmission medium from a coaxial cable to a twisted pair, and vice versa. The biggest advantages of using balanced transmission cables are lower costs, higher resistance to external interferences, and possibility of using longer transmission lines. Due to identical arrangement of the two wires of a balanced line, the interferences are also the same and can be cancelled in a differential balanced input of the receiver. It is not possible in the case of a coaxial transmission line.

The ability of a video transformer to cancel the common interferences identical in both wires is characterized by Common Mode Rejection Ratio (CMRR). It is the ratio of the error signal at the asymmetric output of the transformer to the interference on the both balance inputs. The parameter can be measured, for example, by applying high, common interference signal V_z to the both balance inputs (i.e. shorted, to eliminate a differential signal). Under such conditions, an ideal transformer would not provide any signal on its unbalanced output, but the real device will demonstrate a V_b value. The CMRR is calculated using the following formula:

CMRR = 20*LOG(V_b/V_z)

The CMRR of Etrix baluns (in the 15 kHz to 6 MHz range) is 60 dB. It means that they attenuate the common signals (interferences) 1000 times.