Data transmission

A spread spectrum system for transmitting and receiving binary data, wherein a spread spectrum transmitter includes:

• means for deriving according to a first predetermined recurrence relationship a pseudo-random binary pulse train having a greater bit rate than the data signal at least in part from the data signal;
• means for modulating the pseudo-random pulse train with the data signal to produce an increased bandwidth signal;
• and
• means to phase shift key modulate a coherent RF carrier with the increased bandwidth signal to produce a spread spectrum signal;
• and wherein a spread spectrum receiver includes:
• an input for receiving the spread spectrum signal;
• delay line sections coupled to the input and at least one balanced modulator for combining signals subject to different delays in the delay line sections according to a second predetermined recurrence relationship, the said first second predetermined relationships being such that the delay line sections and at least one balanced modulator derive the said pseudo-random binary pulse train only from the spread spectrum signal, and
• a further balanced modulator having a first input coupled to the said input for receiving the spread spectrum signal and a second input coupled to receive the said pseudo-random binary pulse train derived from the spread spectrum signal to cross-correlate that pulse train with the signal received at the first input to produce a signal comprising the data demodulated from the pseudo-random binary pulse train.