In a cable or CATV system consisting of a central station with a television transmitter connected via a television transmission cable to a plurality of remote stations each with a television receiver, there is provided apparatus for signalling between the central and remote stations. The apparatus includes at the central station pulse generating means for transmitting via the cable variable sets of packets of first frequency signals followed by a packet of second frequency signal. Each of the remote stations is assigned a specific set of the first frequency signals. In each remote station the packets of first frequency signals are converted to a set of first pulses and the packet of second frequency signal to a second pulse. Counting means count the first pulses of the set and if the count at the time the second pulse is received agrees with a count assigned to the remote station an indication is given.