Abstract: Two-way radio communication system with several fixed stations serviced by a fixed dispatching center and with at least one mobile station. The fixed stations transmit at different frequencies and the mobile station at one frequency. The mobile station contains means for hunting the frequency with the best reception and thus receives only the fixed station having the best possible transmission conditions. All stations contain means ensuring that the dispatching center is connected only to the receiver of the fixed station, the transmitter of which is received by the mobile station.

Abstract: A selective calling arrangement for use in a radio communications system or the like. Each of the receivers in the system is assigned an unique binary code number which is transmitted to the receivers by r.f. pulses of fixed width separated by one of two fixed intervals respectively representing a binary "1" or a binary "0", the selective calling system being unaffected by the chopping of pulses on the transmission path.