Patent GB-868770-A (GB)
Title: Improvements in and relating to recording and reproducing apparatus for a telecommunication system
Inventor: DICKMAN MATTHEW COLIN
IPC: H04M1/65
Filed: 1958-10-13
Abstract: 868,770. Substation equipment. DICKMAN, M. C. Oct. 13, 1958 [Oct. 18, 1957], No. 32569/58. Class 40 (4). A recording and reproducing apparatus for a telecommunication system comprises a first signal channel, a second signal channel, and detector means responsive to syllabic signals (i.e. interrupted A.C. signals, such as speech or ring- ing current) in the first channel, wherein the detector means comprises two rectifier circuits, one having a fast-charge/slow.-discharge characteristic and the other a slow-charge/fast-discharge characteristic, the output terminals of the two circuits being so connected that a D.C. output signal is obtained from a syllabic signal in the first channel and a substantially zero output signal from substantially zero or continuous signals in the first channel. As shown, the syllabic detector is used to control the operation of a phonographic device for answering and recording telephone calls. Answering and recording incoming call, Fig. 1. Ringing current on line 5 passes through amplifier 9 and transformer 23 to an arrangement of two rectifier circuits having their outputs in series opposition. One of the circuits, based on condenser 26, has a fastcharge/slow-discharge characteristic, while the other, based on condenser 27, is arranged for slow-charge and fast-discharge. Thus an A.C. input of constant amplitude produces zero output, but a variable input, such as speech current or pulses of ringing current, causes an increase in the anode current of valve 34 so that relay A operates. This brings up relay B, which connects the A.C. mains to recorder 41, loops the line 5 to trip the ringing, and charges condenser 46 through relay C which operates to connect itself in the anode circuit of valve 54. Relay C starts motor 57 and changes the connections of amplifier 9 so that the calling party hears, from a pick-up 58, a pre-recorded announcement on an endless tape driven by motor 57. After one rotation, a metal insert in the tape bridges contacts 255 and 256, connecting the negative terminal 59 of the power supply to the grid of valve 54 which cuts off, releasing relay C to stop the motor 57, restore the connections of amplifier 9, and complete a circuit over lead 234 for the solenoid controlling forward movement of the recorder 41. Any message from the calling party is now recorded, the gain of amplifier 9 being controlled by a volume-compression circuit 66-70. Relay A remains energized as long as line 5 carries speech current, but when speech is replaced by silence or by a steady signal, such as dial tone, the anode current of valve 34 decays until, after a predetermined delay, relay A falls back, followed by relay B, and the apparatus is restored to normal. Reproduction of recorded messages, Fig. 2.- The reproducing unit uses the same power supply 59, 60 as the answering and recording unit, Fig. 1, and controls the same recorder 41. A second telephone line 72, having a directory number known only to the owner, is coupled to the reproducing unit. When the owner dials this private number, ringing current passes through amplifier 80 to a pair of rectifier circuits similar to those shown in Fig. 1. Relays D and E operate to trip the ringing, followed by relay F, which reverses the connection of diode 110, disables the slow-charge/fast-discharge rectifier circuit, and applies a lower bias potential to the grid of valve 92, so that relay D is held operated with no signal on line 72. Now any substantial signal on line 72, such as speech, dial tone, or the sound of the calling party replacing his handset, will cause the release of relay D, providing protection against accidental misdialling of the private number. Relay E also disconnects the power supply over leads 123, 124 to the answering unit, and joins leads 127, 128 to connect the A.C. mains to recorder 41, which begins to warm up. If there is no signal on line 72 for a predetermined period, say fifteen seconds, thermistor 129 reaches a low enough resistance to permit the operation of relay G, which releases relay F, restoring the rectifier circuit connections to normal, and causes stepping relay K to move to position 1 where it completes a circuit over K2 and leads 233, 235 for the rewind solenoid of recorder 41 and maintains over K5 the lower bias on valve 92, holding relay D. When recorder 41 is fully rewound, contacts 132, 133 are closed, completing a circuit over K1 for relay K which steps to position 2. Start, stop and rewind of recorder 41 are now under the control of relays H and J. Each of these relays is operated via a rectifier circuit and a valve (139 or 138 respectively), but relay J is controlled by a filter 140-142 so as to respond only to a particular signal frequency, say 2 kc/s., and not to speech, whereas relay H is controlled by a low-pass filter 143-146 and responds to speech signals but not to the 2 kc/s. signal frequency. If the calling party now speaks, relay H operates. The forward drive solenoid of the recorder 41 is energized over leads 233, 234 and any recorded message is transmitted to the calling party over lead 236. The outgoing speech signals also hold relays D and H. At the end of the message, a period of silence causes relay H to fall back after, say, six seconds. This stops the recorder 41 and switches amplifier 80 to receive incoming signals. The calling party now has time to write notes during the remainder of the release time, say thirty seconds, of relay D. By speaking again he may reenergize relay H and cause the recorder 41 to play back any further message. The calling party may rewind the recorder by sending the 2 kc/s. signal frequency from a tone generator. This holds relay D and brings up relay J to complete a circuit over contacts K2 and leads 233, 235 for the rewind solenoid of recorder 41. Relay J falls back immediately the 2 kc/s. tone ceases. If the rewind is short and relay H is still energized, the recorder resumes playback, giving a back-space effect. Otherwise the recorder stops, and this method may be used to stop the recorder where the space between recorded messages contains dial tone instead of silence. The calling party may resume playback by speaking to operate relay H. When the calling party hangs up, relay D falls back after a delay, followed by relay E which releases line 72 and completes a circuit over contacts K1 for relay K to step to position 3 where contacts K2 complete an energizing circuit for the rewind solenoid of recorder 41. When the recorder is completely rewound, contacts 132, 133 are closed and relay K steps to position O, returning the apparatus to normal. Attachments are described with reference to Figs. 3 (not shown) and 4 (not shown), enabling the apparatus to be used in conjunction with a combined microphone and loud-speaker mounted in a door, so that a personal caller may record a message, and permitting the owner of the apparatus to control its operation, and possibly converse with a calling party, over a channel other than the telephone line 72 (e.g. a radio link). Specifications 421,059, 454,060, 582,735, 628,625, 721,448 and 733,436 are referred to.