Data transmission systems

Claim 1

A data transmission system comprising a transmitting station for transmitting to a receiving station via a transmission line a three-state first data signal comprising pulses of a fixed first duration and both polarities with respect to a datum level interspersed with portions at said datum level characterised in that said transmitting station comprises means (14, 15, T) for converting said three-state data signal (Figure 3A) into a two-state second data signal (Figure 3D) comprising pulses of a fixed second duration less than said first duration, each pulse of one polarity in the first data signal being represented by a pulse in the second data signal, each pulse of the other polarity in the first data signal being represented by the absence of a pulse in the second data signal, and each said datum level portion in the first data signal being represented by a plurality of pulses in the second data signal occurring within a period of duration less than said first duration; and means (T) for transmitting said two-state data signal along said transmission line (16).

Claim 5

A system according to any one of the preceding claims wherein said receiving station comprises: a two-state detector and decoder (17) responsive to the received two-state data signal to produce a signal (Figure 3E) whose waveform is a replica of the three-state data signal between portions at said datum level delayed by the period within which said plurality of pulses occur; a third-state detector and decoder (18) responsive to the received two-state data signal to produce an output (Figure 3F) which changes from a first value.to a second value in response to the occurrence of any pulse in the received signal and returns to its first value only in response to the occurrence of a said plurality of pulses in the received signal; and gating means (G) responsive to the outputs of said two-state and third state detector and decoder to pass the output of the two-state detector and decoder when the output of the third state detector and decoder has its second value, and to produce an output representative of said datum level when the output of the third state detector and decoder has its first value.

Claim 6

A system according to any preceding claim wherein said transmission line is a fibre optic transmission line (16).