Patent GB-1228191-A (GB)
IPC: H04M1/50
Filed: 1968-04-04
Abstract: 1,228,191. Automatic exchange systems and equipment. WESTERN ELECTRIC CO. Inc. 4 April, 1968 [5 April, 1967], No. 16242/68. Headings H4J and H4K. A V.F. key sender for use with an exchange having abbreviated dialling facilities comprises a tuned circuit which on operation of any key is caused to generate a first frequency which is common to all the keys and thereafter is caused to generate a second frequency which is unique to the particular key operated. The first frequency acts as a prefix signal for accessing the exchange store containing the full directory numbers of a plurality of subscribers and the second frequency acts as an address signal for accessing a particular one of these directory numbers. In practice the first and second frequencies each comprise two, three or more frequencies.  As shown, the frequency generator comprises two tuned circuits 52, 54 in each of which a capacitor 55, 62 respectively is connectible to one of a number of taps on coils 56, 64 in dependence on the particular key 14 (normal key sending) or 15 (abbreviated dialling) that is operated. Actuation of a "normal" key 14 additionally operates switch 19 so as to, sequentially, mute receiver 46, disconnect transmitter 45, energize amplifier 70 and shock-excite the two tuned circuits (opening of contact 22). The excitation is maintained by inductive coupling between coils 56, 64 and coils 76, 78, 80 and 82 in the amplifier. The oscillations generated by the tuned circuits are coupled via an induction coil 29-32 to line. The variators are used as follows: 35 for line length compensation; 33 as a non-linear impedance in the antisidetone network 37; 60, 66 for amplitude limiting of oscillations in the tuned circuits; and 86 for development of base bias for transistor 68 (capacitor 88 acts to prevent parasitic high frequency oscillation). Abbreviated dialling.-Actuation of any one of keys 15 initially connects capacitors 55, 62 across predetermined portions of coils 56, 64 by closing contacts 26, 27, closes at contacts 28 a charging circuit for capacitor 92 in a delay circuit 90 and operates switch 19 whereby the sequence of events outlined above takes place. A first frequency combination is thus transmitted to line until transistor 94 turns-on (after 40 msecs) and thereby effectively short circuits the tuned circuits by closing a relay contact II. Relay contacts 12 complete a charging circuit for a capacitor 98 whereby 40 msecs later transistor 100 turns-on and brings up relay 0. The latter connects capacitors 55, 62 to the taps on the coils pertaining to the still-operated key and by opening its contact o5 allows a new frequency combination to be generated and sent to line. At least 40 msecs. later, the key may be released so as to restore the circuits to normal. Abbreviated dialling, alternative embodiment (Fig. 3, not shown).-In this alternative, a controlled rectifier is inserted in series with each tap on the coils 52, 64 and the keys 15 are connected to the gates of particular ones of these rectifiers. Provided a key is actuated for at least 40 msecs, the appropriate rectifiers will turn-on so as to "memorize" the identity of the key during "dialling" and the key may then be released. Desk set (Fig. 1).-The names of subscribers who can be reached by abbreviated dialling are recorded on tags 16 which are accessible upon removal of cover 13.