Method of transmitting information by radio

System for selectively alarming persons, having a transmitter and a plurality of receivers, the transmitter comprising:

• input means controllable for defining a first digital information selectively associated to a person to be alarmed, and a second digital information to be transmitted to said person,
• binary encoding means for converting said first and second digital information into a first binary sequence for calling and a second binary sequence for information and,
• means adapted to transmit pulses of electromagnetic radiation, in the form of a calling sequence of pulses having an initial pulse, followed by a predetermined number of pulses of duration t1 or t2, depending on said first binary sequence, and of a sequence of information having a starting-information pulse followed by the same number of pulses of duration t1 or t2, depending on said second binary sequence, with the initial pulse and starting-information pulse both having a duration greater than t1 and t2, and the initial pulse further having a duration greater than that of the starting information pulse;
• and each receiver comprising:
• receiver means to receive said electromagnetic radiation and recover the pulses thereon,
• a first monostable multivibrator coupled to the receiver means and operative upon the leading edges of each output pulse of the receiver means to deliver first reference pulses having a duration comprised between t1 and t2,
• shift register means receiving both said pulses of duration t1 or t2 and said first reference pulses for sequentially storing one or the other binary state upon each pulse of the sequence when its duration exceeds or not the duration of the simultaneous reference pulse, respectively,
• a decoding matrix being coupled to a first portion of the shift register means for delivering an output indicating when said first portion of the shift register means contains a predetermined sequence of binary information associated to the receiver,
• warning means responsive to said output indication of the decoding means,
• a second monostable multivibrator coupled to the receiver and operative upon each leading edge of an output pulse thereof to deliver a second reference pulse having a duration greater than both durations t1 and t2 but lower than the duration of said initial pulse and said information-starting pulse,
• first logic gate means connected to said receiver means and second monostable multivibrator, to give an output indicating the part of the duration of an incoming pulse in excess of that of the simultaneous second reference pulse, the first logic gate means being coupled to said shift register means to reset it when a received pulse exceeds the duration of said second reference pulse,
• a bistable means coupled to the output of the decoding matrix for being set when said output indicates the predetermined sequence being contained in said first portion of the shift register,
• means coupled to the output of the first logic gate means to discriminate said initial pulse from said starting-information pulse and to reset the bistable means in response to the initial pulse,
• an alphanumerical display means,
• another decoder having an enabling input and being coupled between a second portion of the shift register means and the alphanumerical display means to decode the binary information of the shift register means and correspondingly control the alphanumeric display means, and
• second logic means connected at least to said bistable means and coupled to said other decoder to enable it when the bistable means is set, indicating that a sequence of information is received.