Patent GB-418004-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q5/08
Filed: 1933-04-21
Abstract: 418,004. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and MOSS, B. F., c/o General Electric Co., Stoke, Coventry. April 21, 1933, No. 11674. [Class 40 (iv).] Wanted numbers are transmitted by calling subscribers by senders controlled by keys or the like which cause alternating or pulsating currents, of frequencies or frequency combinations representing the digits, to flow over the subscribers' lines. The alternating currents may be generated by reeds, forks or mechanical resonators in conjunction with an auxiliary microphone or normal microphone at the substation, or these currents may be supplied from the exchange, the frequencies transmitted being determined by filters controlled by the keysender. Arrangements for translating the alternating current impulses into marking potentials, for example, for controlling the selectors may be provided, and a common translator may be used at each selecting stage. In the registercontroller system shown in Fig. 1, however, an A-digit switch 37 and an auxiliary register 33, which may be similar to that described in Specification 219,079, [Class 40 (iv)], become associated over switch 32 with the calling line 28, and a switch 34 associated with register 33 hunts for a translator 35 which may comprise tuned relays or relays operated by gas-discharge triodes as described in Specification 373,383. The digits from the translator are stored in relay groups in register 33 and are then transferred by a sending switch to the A-digit switch and register-controller 39. In systems not using register-controllers, the switches are directly impulsed from the auxiliary register 33 which may have an individual translator 35. Dial tone may be replaced or accompanied by current reversal which operates a polarized relay to unlock the sender, the reversal being removed when all the digits have been sent. An exchange may have subscribers with dial transmitters as well as subscribers with voice-frequency transmitters connected to different groups of finders and first selectors, thevoice-frequency translating arrangements being provided where necessary ; alternatively, the both classes subscribers have access to the same switches, a discriminating signal from the line circuit being sent when voice-frequency arrangements are required for use. According to the Provisional Specification the key sets may be used by operators. Constructions of impulse sender. In the first arrangement, Figs. 3 and 4, intended to replace a standard dial transmitter, a body portion 10 has four circular tracks 3-6 each containing sets of balls 9 and spacers 11 freely movable in the tracks and pressed towards the closed ends of the tracks by springs 63. The spacer at the free end of each set, or a pivoted plectrum 12 carried thereby is adapted to pluck one of a set of reeds W-Z carried by a member 64 mounted in felt or rubber pads 65 in the body portion and connected to an auxiliary microphone 66 by a stem 70. The member 64 may be the diaphragm of the microphone. The instrument is provided with ten keys each consisting of a portion 14 sliding in the body 10 and carrying one or more pointed pegs 20 located above a pair of balls so that when a single key is pressed a peg or pegs enter between the balls and the plectrum 12 of one or more of the sets is moved counterclockwise and engages the set of reeds. When a plectrum comes against a fixed stop 61 it releases the corresponding reed and a corresponding voice frequency is sent to line by microphone 66. When the key is released, the balls and spaces are moved back to normal by spring 63 and the plectrum is re-positioned by a fixed stop 62. The reeds may normally be damped by a pad 67 carried by a spring controlled member 69 which is forced down to free the reeds when a key is pressed. Or, separate damping pads for each reed may be freed when the spacers carrying the plectra are moved by the keys. Alternatively, an extra track and an extra pin on each key may be provided, the balls and pins being so arranged that only one key at a time can be depressed, the movement of an end ball being utilized to free a common damping pad. In the modified sender shown in Figs. 7 and 8, a row of key levers 71 are pivotally mounted at 75 and each lever carries one or more hooks 74 adapted, on depression of a key, to pull down one or more U-shaped bars 73 pivoted at 76. Each bar 73 carries an inclined trigger 77 which, during downward movement of a bar, rotates and releases a spring controlled hammer lever 80 to strike a tuning fork 87. A set of forks 87 is carried by a member 86 mounted on the body of the sender and connected to auxiliary microphone 66. The keys may be arranged in two or more rows as in a typewriter, and a further bar 73 (not shown) may be operated to free a damping pad when any key is pressed and operate electrical contacts if necessary. In other modifications, the forks may act acoustically, and not mechanically, on the auxiliary microphone, or in the case of a telephone set having a transmitter fixed to the base, the auxiliary microphone may be dispensed with by mounting the forks &c. on the base, or the forks &c. may be struck by linkwork as employed in typewriters. The auxiliary microphone may be switched out during conversation.