Patent GB-793991-A (GB)
IPC: H04W84/02
Abstract: 793,991. Radio signalling. WESTERN ELECTRIC CO., Inc. March 6, 1956 [March 16, 1955], No. 6997/56. Class 40 (5). A radio telephone system comprises a central station with a radio transmitter and receiver, a plurality of dispatcher's stations connected thereto, said central station including means responsive to a call from any dispatcher's station for connecting said station to the central transmitter and means responsive to the initiation of said call for transmitting a tone individual to said dispatcher's station for calling a fleet of mobile units individual to the said dispatcher's station, said central station also including automatic means for registering a call waiting responsive to a call from any of the said stations while the system is busy, and automatic means for completing all calls waiting in a predetermined sequence. System Idle.-A circuit exists from the battery, through the bottom winding of relay L Fig. 1, winding W1 of repeating coil RC, contact 5 of relay RY and conductor R1 to the distant dispatcher's telephone circuit, which is normally open, except for the usual bridged ringing means. The return circuit is through T1, contact 3 of relay RY, winding W2 of the repeating coil RC and the top winding of relay L to ground. Call originated by a dispatcher-system idle.- When a dispatcher lifts his handset relay L, Fig. 1, operates, which in turn operates relay LA, Fig. 1, connecting the dispatcher's telephone circuit to the line to the radio station through the contacts of relay TO, Fig. 2. Relay L also operates relay TR which in turn operates slow releasing relay TO, Fig. 2, thus connecting the line to the base radio station to the output of amplifier V2, preparing the circuit for transmission of the channel identification tone, supplied by relay LB, Fig. 1. The operate path for relay TR is opened by relay CR1, Fig. 5, to permit slow releasing relay TO to release. A holding path is, however, established for relay TR through relay AT, Fig. 3, to replace the ground through contact 2 of relay L, Fig. 1, after relay CR1 operates. After the carrier is on relay AT operates and since relay TO is slowreleasing a tone is transmitted for 0.3 sec. after the carrier is on. Relay LA, Fig. 1, also operates relay ET1, actuating the elapsed time meter ETM1. Relay LA also operates relay MD, Fig. 2. Relay LA also operates relay LB, Fig. 1. A holding path to ground is maintained by relay LA on operation. Relay LA also operates relay PR1, Fig. 5. The operation of relay MD, Fig. 2, disconnects ground, through key " Talk," Fig. 3, of all the relays, e.g. relay K1, Fig. 8, in all the tone-operated switches, Figs. 8, 10, preventing any mobile unit from signalling any dispatcher once the latter has control of the system. Relay LB, Fig. 1, also connects the output of the first tone generator, Fig. 9, to the input to the amplifier V2, Fig. 2, through amplifier A, Fig. 4, to the radio transmitter RTS, Fig. 4, transmitting the tone individual to channel 1. Relay LB establishes a circuit from ground to contact 4 of relay PR1. When slow releasing relay PR1 operates the circuit is extended to prepare relay BL, Fig. 3, to start the transmitter, delayed until relay TO is operated. Simultaneously relays S and V, Fig. 2, are released, operating relay PR1 associated with channel 1. Relay PR 1 operates relay RA, Fig. 6, and also, before relay RA operates, operates relay CR1. Relay PR1 also operates relay BL. Relay RA now operated establishes a circuit through contact 4 of all relays such as CR2 and CR3 corresponding to contact 3 of relay CR1, and circuits extend through elements in the other channel circuits operating all relays comparable with relay RV of channel 1, in all channels other than Channel 1. If any other dispatcher attempts to make a call his relay L will operate, operating relay DR, and his RV relay will connect the busy tone supply BTS and B.G., Fig. 8, to his line. Relay CR1 of the user opens the operating path of relay TR, Fig. 2, and holds relay PR1. When any CR relay, other than CR1, operates, the battery supply to all other PR relays is disconnected, and cannot operate. Relay BL, Fig. 3, operated, operates the anode control relay of transmitter RTS (not shown) starting RTS, which when radiating, by its monitor relay (not shown) operates relay AT, which in turn releases relay TR, Fig. 2. Relay TR, released, opens the operating path for slow releasing relay TO, which has a 0.3 sec. release time. Relay TO effects the modulation of the transmitter with the individual dispatcher's tone for 0.3 sec. before it releases, thus energizing the mobile units of the dispatcher's fleet, each of which receiving units employs a known squelch or muting circuit. When the called unit answers, the squelch circuits of the other mobile units are reset thus: relay BL, Fig. 3, operated, also operates slow release relay CO, opening the parallel branch through the contact of relay CO. When the mobile unit receives a call, its push-to-talk button is operated, transmitting a carrier which operates a codan relay (not shown) at the base station, which in turn operates relay CA. Relay CA operates relay E, Fig. 3, interrupting the transmitter RTS. Relay E also makes relay CO release slowly, restarting the transmitting carrier. Relay E is maintained and in its turn maintains relay CO released. Thus the carrier from RTS cannot be interrupted by a mobile station. The momentary interruption of RTS resets the squelch circuits of all mobile units in the fleet except the one designated, whose squelch control circuit is disconnected when the handset is removed from its hanger. Call originated by mobile unit-system idle.- The mobile unit, operated by the press-to-talk button, transmits a burst of identifying audiofrequency tone characteristic of its fleet, which when received by RRS, Fig. 4, is passed to the input of a selective audio amplifier, corresponding to F. AMP, Fig. 8, with a vacuum tube operated relay K- responding to the particular audio-frequency tone. If the unit belongs to the first fleet relay K1 will respond, operating relay MR, Fig. 1, which in turn operates relay CW, relay CW operates relay PR1. Relay PR1 operates relay RA, Fig. 6, in turn operating relay RB. Relay PR1 also operates relay CR1, relays MR and CW being maintained by a holding circuit. Relay MR operated, operates relay RV, Fig. 1 ringing the called dispatcher with a first type of ringing signal, identifying the call as incoming from a mobile unit of his fleet. Relay CR1 operated, also operates relay RY which establishes a circuit to ground through interrupter INT, Fig. 7, which operates relay SC once per second; relay SC operating relays SA and SB, Fig. 2, alternately. When relay SA is operated it is held, and ringing current is supplied from source ACDC. Relay RGR operates during each one-second interval. Relay RY also operates relay TO, which operates relay BL, Fig. 3, starting transmitter RTS, Fig. 4. Relay TO, operated, connects the output of the last tone generator LTG, Fig. 9, to the input of amplifier V2, Fig. 2, whose output is applied to the transmitter RTS; thus each ringing cycle modulates the transmitted carrier. A different frequency tone is used to call each fleet. If the dispatcher does not answer within 40 seconds the ringing is automatically stopped by a timing circuit associated with relay NU, Fig. 6. When the dispatcher answers a relay, TP, Fig. 1, passing alternating current but operating on D.C., operates, being provided with a D.C. potential from relay SA during both the ringing and silent intervals, permitting operation during both. Relay TP releases relay RY, Fig. 1, removing the ringing generator from the line, and locks to ground. When relay RY releases, relay L operates, operating relay DR, which is then locked, and opens the operating path for relay RV, Fig. 1, operating relay LA, and in turn relay LB, Fig. 1. The call is then completed as previously described. However, relay TO does not operate; and relays CW and MR release, and relay RV is locked until relays L and LA have operated. When the dispatcher hangs up all relays restore to system idle conditions. Call originated by dispatcher-system busy.- When the dispatcher, say channel 1, calls, his L relay operates and since relay RV is operated, relay DR will operate, operating relay CW. Relay CW operated, operates relay PR1. Relay CW also establishes a circuit through the winding of relay V, Fig. 2. Relay CW is in the released condition, and relay LA appropriate to the communicating channel will be operated, extending the circuit to operate relay V. Relay V maintains relay PR1 operated, and arranges timing circuit (relay T, Fig. 2) for a 15-second waiting period on completion of the call in progress. When the channel waiting is assigned to the system, the relay corresponding to relay CR1 operates, which in turn operates relay RY, and relay RV releases. Relay RV released connects a distinctive machine ringing generator circuit RC2, Fig. 7, to the circuit of the waiting dispatcher. When the call is answered, relay TP operates, releasing relay RY, disconnecting the ringing generator. When relay AT, Fig. 3, is released, relay TR operates and relay TO operates, transmitting the channel identification tone. Relay TR is locked and cannot operate when relay MR operates in response to a call from a mobile unit. When relay LA is operated relay CW releases. Enforced fifteen second idle circuit condition.- At the end of each waiting call a 15-second enforced idle circuit condition is established to enable waiting units to gain access, during which an attention tone is radiated. When the sytem is in use the CW relay is released in the user's channel, and the CW relays registering calls waiting are operated and relay V is operated, preparing relays PR1 and CR1. Relay V also operates relay S, which becomes locked. When the call is completed relay V releases, all non-locked re