GB1471318A - Communication apparatus for receiving data - Google Patents

Abstract

1471318 Radio telephone systems INTERNATIONAL MOBILE MACHINES CORP 14 June 1974 26471/74 Headings H4L and H4J A radio telephone system, includes a duplexer 16 and a conventional FM receiver and transmitter 12, 14 respectively for communication with a base station. To initiate a call the handset is removed from its hook to close a switch 41, Fig. 1, and open the circuit of line 42. Thus causes a scanner 36 to scan through the available channel frequencies and lock on to an idle channel which carries a 2000 Hz idle tone which is selected by filter 24 and passed to the scanner and to a gate 64. At the same time the impulse on line 42 turns on transmitter 14 and is also passed to a timer 52 which activates a 2150 Hz oscillator 54 for 250 milliseconds to modulate the transmitter accordingly. The signal from line 42 also enables an AND gate 60. The signals from the base station include the 2000 Hz idle tone and an 1800 Hz data tone for the particular user of the apparatus shown and these signals are passed to a decoder 30 which is arranged to separate tones and digits corresponding to the particular user from incorrect tones and digits which latter are supplied via line 32 to restart the scan. The 1800 Hz tone is selected by filter 26 and supplied to the decoder 30, to AND gates 60, 64 to cause them to conduct and to transmitter 14 to inhibit it from sending. AND gate 64 operates an alarm 76 and maintains the muting at 20. AND gate 60 operates a pulse encoder 80 which turns on transmitter 14 and sends a pulse via inverter 86 to sequentially operate encoder oscillator 54 and encoder disconnect 94 to send a signal to the base station for billing purposes. The output of encoder 95 also provides a signal to maintain circuit 20 in the unmuted state. The multi-frequency signalling pad 96 is then operated to dial a required number and communication is established via the microphone and receiver of the handset. When the handset is replaced on the hook a pulse is sent to the scanner 36 which resumes scanning and to a timer 102 which operates a flip-flop 104 to deactivate the encoder 54 and encoder disconnect 94 and turn off transmitter 14 via timer 116. Portable transmitter-receiver.-A housing 212 is provided with a handle 214 which is pivoted at 216 and may be locked in the closed position by a latch 218. A shelf 220 in the housing carries a multi-frequency signalling pad 222. This may be replaced by a dial or other pulse-generating system. The radio and encoding decoding equipment 226 is beneath the shelf. The handset 228 is held within the handle by a clip or hook 234 and when the handset is removed it releases a button 236 to activate the system. An aerial 240 in the handle is in the operative position when the handle is open.