Data transmission systems

Claim 2

A transmitter in a data transmission system, comprising: a data store for providing a unipolar binary data stream; a clock source for providing a sinusoidal carrier wave of a predetermined frequency; means responsive to said carrier wave for converting the unipolar binary data stream into a bipolar data stream at a bit repetition rate corresponding to the predetermined frequency of the carrier wave and modulating said bipolar data stream with said carrier wave for forming, for each binary zero digit of the binary data stream, a corresponding signal-less interval, and, for each binary one digit of the binary data stream, a corresponding sinusoid which is alternately normal and inverted for successive binary one digits of the binary data stream; means responsive to the carrier wave for adding a first pilot wave to the modulated output of said converting and modulating means; and means for applying the resulting combination of the carrier modulated bipolar data stream and the first pilot wave to the transmission medium of the transmission system.

Claim 3

A transmitter according to claim 1, wherein said clock source is arranged to generate the clock signal in synchronism with the carrier wave, and said data store supplying said binary data stream at a bit repetition rate determined by the clock signal.

Claim 4

A transmitter according to claim 2, wherein the clock signal is used as the first pilot wave and is in phase quadrature with the sinusoids.

Claim 5

A transmitter according to claim 3, wherein the first pilot wave is of smaller amplitude than the amplitude of the sinusoids.

Claim 6

A transmitter according to claim 4, including means for transmitting first and second auxiliary pilot waves of different frequencies wherein the frequency of the first auxiliary pilot wave is an integral multiple of that of the second.

Claim 7

A transmitter according to claim 5, wherein the first auxiliary pilot wave is constituted by the first pilot wave.

Claim 8

A transmitter according to claim 1, wherein for each binary one digit of the binary data stream, a corresponding signal-less interval is formed, and, for each binary zero digit of the binary data stream, a corresponding sinusoid which is alternately normal and inverted for successive binary zero digits of the binary data stream is formed.

Claim 9

A receiver in a data transmission system, for receiving an incoming data signal comprising a binary data stream modulated by a carrier wave wherein each binary zero digit or the data stream is represented by a period of the carrier wave, and binary one digits of the data stream are represented by sinusoids which are alternately normal and inverted for successive binary one digits of the data stream, comprising demodulating means for recovering the binary data bit stream from the data signal, said demodulator means further including means arranged to receive together with the data signal a first pilot wave which has the same frequency as the carrier wave, the pilot wave being supplied to the demodulating means to effect demodulation of the data signal said demodulator means also further including means to receive together with the data signal, first and second auxiliary pilot waves of which the frequency of the first is an integral multiple of the second, said receiver further including a mixing circuit responsive to the auxilliary pilot waves and arranged to be responsive thereto and generate a timing wave of frequency equal to the repetition rate of the carrier wave.

Claim 10

A receiver in a data transmission system, for receiving an incoming data signal comprising a binary data stream modulated by a carrier wave wherein each binary zero digit or the data stream is represented by a period of the carrier wave, and binary one digits of the data stream are represented by sinusoids which are alternately normal and inverted for successive binary one digits of the data stream, comprising demodulating means for recovering the binary data bit stream from the data signal, said demodulator means further including means arranged to receive together with the data signal a first pilot wave which has the same frequency as the carrier wave, the pilot wave being supplied to the demodulating means to effect demodulation of the data signal said demodulator means also further including means to receive together with the data signal, first and second auxiliary pilot waves of which the frequency of the first is an integral multiple of the second, said receiver further including a mixing circuit responsive to the auxilliary pilot waves and arranged to be responsive thereto and generate a timing wave of frequency equal to the repetition rate of the carrier wave.

Claim 11

A receiver according to claim 8, wherein the first auxiliary pilot wave is constituted by the first pilot wave.

Claim 12

A receiver according to claim 9, including a sampling circuit arranged to sample, in accordance with the timing wave, a signal derived from the demodulated signal, and also including a testing circuit responsive to the demodulated signal to generate timing signals indicating when the sampling circuit is required to effect the sampling, and a control circuit responsive to the timing signals to vary the phase of the timing wave so as to tend to effect the said required sampling.

Claim 13

A receiver according to claim 10, wherein the testing circuit is arranged to combine the demodulated signal and a signal derived from the demodulated signal but delayed relatively thereto by a predetermined amount and to test when those combined signals exceed a predetermined amount.

Claim 14

A receiver according to claim 11, wherein said delay is equal to two periods of the said repetition rate.