Patent GB-506865-A (GB)
Abstract: 506,865. Semi - automatic exchange systems. TELEPHONE MANUFACTURING CO., Ltd., PADDLE, L. H., and FLINT, J. G. Sept. 2, 1937, No. 24017. [Class 40 (iv)] A system of alternating current signalling between exchanges employs two frequencies, one of which is voice-immune, that is, not liable to imitation by voice currents, while the other, which is used for impulsing, is not voice-immune, and it is arranged that, during conversation, the impulsing frequency is effective only if it is accompanied by the voiceimmune frequency. The voice-immune frequency X may for example be 750 cycles interrupted at 17 cycles and the impulsing frequency Y 600 cycles. The signalling frequencies may modulate a carrier if carrier working is employed. The Figure shows the apparatus at either end of a 4-wire junction to which the frequencies X, Y are applied by the operation of relays XS, YS. The signal detector controls relays XR, Y, YR, and, during conversation, relay ES is operative, so that relays Y, YR can respond to frequency Y only if relay XR is operated by frequency X. Calling and impulsing. When the operator plugs into jack JS, sleeve relay S connects up CO, CS, and the switch M steps through postions 1-6 in which XS sends a long X pulse to position 7 in which CS falls back. At the called end, XR responds and connects up RA which closes the loop to the incoming selector, and'at the end of the pulse RB operates and connects up CS momentarily to step the switch M to position I, a short Y pulse being reverted by YS. Relays Y, YR respond at the calling end and connect up AK, ES which lock and flash the supervisory lamp. The insertion of the dialling plug in jack DKS operates DK, DKR and places YS under the control of the dial The dialled impulses are repeated to the selectors at the called end by Y, dialling relay C being operative in the usual manner. On the removal of the dialling plug, DKR remains up and CS operates to step the switch M to position 13, XS sending a long X pulse in positions 7-12 and YS a short Y pulse in position 10. At the called end, since XR, YR are up together, RD operates followed by RE when YR falls back, whereupon ES energizes and locks. Supervision and release. On the reply of the called party, relay D energizes followed by AR which connects up CS to step the switch M to position 7, XS sending a long X pulse in positions 1-6 and YS a short Y pulse in positions 4, 5. At the calling end, since XR, YR are up together, P energizes and locks in series with AS. Earth is connected to the ring wire when XR falls back, and the supervisory lamp is extinguished. The relapse of D when the called party hangs up sends back X frequency continuously, and the operation of XR relights the supervisory lamp. When the operator clears, S, CO, ES fall back and F pulls up, sending X and Y frequencies continuously and putting AK under the control of YR only. This signal disconnects RA at the called end to allow the selectors to restore, whereupon YS operates over normal contact NS to send back Y frequency in addition to the X frequency already applied, so that AK, F'relapse at the calling end and out off the releasing signal. Relays RB, ES, AR fall back at the called end. Calling the distant operator. The calling operator inserts in the dialling jack DKS a plug which supplies battery to operate TA. Whether this occurs before or after dialling, CS advances the switch M to position 19, a long X pulse being sent in positions 13-18 and two short Y pulses in positions 16, 18. At the called end, the first Y pulse connects up RD, RE, ES, like the end of dial ing signal, and the second connects up TB, CO to transfer the connection to the jack JS, the line lamp being flashed and ringing tone being reverted. Upon plugging in, S disconnects TB, and D connects up AR. If the called operator clears first, release takes place as described above. If the calling operator clears first, the releasing signal sent by the operation of F lights the supervisory lamp at the called end, but RA is held by S until the called operator clears, when Y frequency is reverted to cut off the releasing signal. Reference has been directed by the Comptroller to Specification 489,545.