Digital video and data transmission

Apparatus for transmitting digital video data and auxiliary data over a four twisted wire pair cable, comprising:

• a transmitter including differential mode circuitry arranged to transmit a first, second and third digital video colour signal and a digital video timing signal as differential mode signals over the four twisted wire pair cable;
• and
• a receiver including differential mode circuitry arranged to receive the differential mode signals, and
• wherein the transmitter and the receiver further include common mode circuitry arranged to provide a data channel for sending auxiliary data between the transmitter and the receiver using common mode signalling over selected first and second twisted wire pairs of the four twisted wire pairs of the cable, the common mode circuitry including, at the transmitter, a first common mode choke connected to the first twisted wire pair and a second common mode choke connected to the second twisted wire pair, the first and second common mode chokes each being wired in antiphase, the common mode circuitry further including, at the receiver, a third common mode choke connected to the first twisted wire pair and a fourth common mode choke connected to the second twisted wire pair, the third and fourth common mode chokes each being wired in antiphase, and
• wherein the first, second, third and fourth common mode chokes are arranged to insert or extract auxiliary data signals onto or from the selected first and second twisted wire pairs and to output the auxiliary data signals extracted using said common mode chokes.