Patent GB-378925-A (GB)
Title: Improvements in or relating to radio-signalling systems
IPC: H04B1/54
Filed: 1931-04-08
Abstract: 378,925. Electric signalling and remote control systems. RICCHIARDI, P. C., 1, Via Montecuccoli, Turin, Italy. April 8, 1931, No. 10388. Convention date, April 9, 1930. [Class 40 (i).] In a wireless signalling system, low-frequency currents modulate an intermediate frequency which in turn modulates a carrier frequency, two intermediate frequencies being used, one for calling and reply signals and the other for the transmission of a message, and each signal to be transmitted consists of three low frequencies sent in succession, these signals being used to position three condensers at the called station to produce low frequencies which are responded to by the calling station. Figs. 1 and 2 show the transmitting and receiving equipment with a common aerial and changeover switch operated by relay 67. The aerial is normally connected to the receiving system comprising a first detector VI, Fig. 2, a second detector V2 (the tuning of which can be varied by the relay 72), and an output valve V3 controlling a relay 4 having three reeds 61, 6<2>, 6<3> tuned to different frequencies adapted to close the circuits of magnets 10<1>, 10<2>, 103 operating selector bar mechanism controlling a typewriter and also means for setting condensers and giving the reply signal. The transmitting system comprises a valve 107 generating the carrier wave and modulated by oscillations of intermediate frequency from a valve 108, which is in turn modulated by a beat heterodyne 113, comprising valves 115,116. The beat frequency is varied for calling and signalling purposes by connecting one of the condensers 39<1>, 392, 393 in the grid circuit of valve 115, this being effected by relays 137 under the control of a distributer 117 and keyboard K. Transmission of calling signal. The condensers 39<1>, 39<2>, 39<3> are first set to. give the low frequencies to which the wanted station responds and key 101 depressed which causes relay 67 to connect the aerial to the transmitter. The number of the calling station is then transmitted by depressing successively three keys of the keyboard. The depression of each key, say 106<1>, starts the distributer 117 which successively completes circuits from the contacts 130<1>, 130<2>, 130<3> of the key 106<1> through the relays 137, so that a permutation of these relays characteristic of the key 106<1> is energized and causes the transmission of corresponding low-frequency modulations of the " calling " intermediate frequency. During the rotation of the distributer the other keys are locked by a magnet 134, Fig. 1 (and Figs. 9 and 10, not shown). At each rotation the distributer energizes a magnet 167 controlling a toothed rack 170 so that when the signals corresponding to three keys have been sent, a projection 171 on the rack energizes a self-locking relay 176 which brings an additional condenser 112 into the circuit of the intermediate oscillator 108, thereby altering the intermediate modulation frequency to that used for transmitting the message. The projection 171 on the rack 170 also energizes a relay 103 which de-energizes the change-over relay 67 so that the aerial is connected to the receiver ready to receive the reply-signal. Reception of call and transmission of reply signal. The received signals selectively erergize the magnets 10<1>, 10<2>, 10<3>. The energized magnet 10<1>, Fig. 7, say, attracts its armature 11 and releases three of the rods 12<1> .. 12<9>, which tend to move to the right under the action of springs 13. The bar 14, assuming that rods 121, 12<2>, 12<3> have been released, permits the movement of rod 12<1> only which raises bar 14 through a bell-crank lever to allow rod 12<2> to be displaced. If the second and third incoming impulses have the same modulation frequency, rod 12<2> is displaced by the second, the bar 14 being again raised, and rod 12<3> by the third. These three rods are displaced by an amount equal to the pitch of teeth 15<1> formed on them and type bar 16<1> is allowed to fall into the row of aligned slots, Fig. 4. Displacement of rod 12<3> closes contacts 17<3>, energizing the printer magnet 19 whose armature 21 engages type bar 161 previously lowered. Any of the type bars may be actuated by a combination of three modulation frequencies corresponding to the three reeds and after printing, relays shown in Fig. 7 return rods 12<1> &c. and bar 14 to their normal position. At each energization of the printing magnet 19, the rack 26 is moved one step so that when the three digits of the calling station have been received, the projection 68 on the rack 26 closes a circuit for the relay 72 which brings an additional condenser C2 into the circuit of the intermediate rectifier V2, thereby altering the intermediate modulation frequency to that used for communication. The circuit of relay 72 is maintained by a selflocking relay 34, which also restores the rack 26 and opens the circuit of magnet 42, Fig. 1, over the connection Z, the function of which is described later. The first ten of the type bars 161 &c. also control circuits X for ten magnets 371, Fig. 1 (and Figs. 5 and 5a, not shown), which control stop members to adjust the condensers 39<1>, 39<2>, 39<3> to such positions that they subsequently transmit frequencies corresponding to those responded to by the receiver of the calling station. When the type bar corresponding to the first digit of the calling station is selected and the corresponding magnet 37<1>, say, energized, the printing magnet 19 energizes over circuit Z a magnet 42, Fig. 1, which, through a rack and pinion 44 moves all three condensers 39<1>, 39<2>, 39<3> until arrested by the stops controlled by magnet 37<1>. The magnet 42 also moves a rack 53 one step so that a circuit is closed over contact 51<1> for 50<1>, which closes a holding-circuit and locks the condenser 39<1> in its adjusted position, the other condensers 39<2>, 39<3> being free. When type bars corresponding to the second and third digits are selected, the magnet 42 is again energized and condensers 39<2>, 39<3> adjusted in a similar way, locking magnets 50<2>, 50<3> being energized. When the condensers have been set, the rack 53 engages contact 513 thereby energizing magnet 57 which restores the rack and energizes a magnet 59 which depresses a special key lever 106<27>. The depression of this key causes the aerial to be connected to the transmitting equipment and starts the distributer 117, causing the transmission of a signal, in the manner previously described, the group frequencies of which are determined by the setting of the condensers. When the reply signal has been sent the aerial is automatically connected to the receiving equipment and the transmission of the message effected on the second intermediate frequency.