Abstract: Data transmission system comprising a data transmitter (1) including:swept frame display means (2), anda generator of composite video signals (20, 22) to control the operation of said swept frame display means (2); anda portable information detection device (7) for receiving said transmitted data by said data transmitter (1).The data transmitter (1) further comprises means (23) for modulating at least one of the elementary signals constituting said composite video signals with the data to be transmitted, and said information detection device (7) further comprises any inductive antenna (44, 45) for detecting said modulated elementary signal.

Abstract: A highly stable frequency generator (G) comprises an oscillator (10) for generating a first frequency (F1), andfurther comprises a time base (BT) providing a time stable frequency signal which is independent of the temperature, and a feedback circuit arranged to provide a first number of pulses (n.sub.T) coming from the oscillator (10) to a comparing circuit (13), a circuit (14) for providing a reference number of pulses (N.sub.T) to said comparing circuit (13), and a circuit (13,15,16) providing a correction signal (Sc) as a function of the difference (.DELTA.) between the first number (n.sub.T) and the reference number (N.sub.T), the generator (G) further comprising a correction circuit (17) of the oscillation frequency (F1) of said first oscillator (10), this correction circuit being controlled by said control signal (Sc).