. The Bell System technical journal . essential elements of the circuit are shown in Fig. 8. It connects to thetrunk relays over two leads e and m and into the line circuit via leadslabeled t, r, Ti and Ri . The transmitter, shown in the upper portion ofthe figure, uses dc biased germanium varistors (diodes) to control theapplication of signal current to the line, and for control functions, usesfour relays designated m, co, hl and rr. The functioning of the firstthree except for tone control are described under the heading Descrip-tion of 2,600 Cycle Design later in this article. The rr relay
. The Bell System technical journal . essential elements of the circuit are shown in Fig. 8. It connects to thetrunk relays over two leads e and m and into the line circuit via leadslabeled t, r, Ti and Ri . The transmitter, shown in the upper portion ofthe figure, uses dc biased germanium varistors (diodes) to control theapplication of signal current to the line, and for control functions, usesfour relays designated m, co, hl and rr. The functioning of the firstthree except for tone control are described under the heading Descrip-tion of 2,600 Cycle Design later in this article. The rr relay (not shown)in conjunction with the m relay lengthens the sent pulse for the ring for- Table V Dialing Condition Talking Condition 1,600 2,600 1,600 2,600 Sensitivit3% dbm Bandwidth, cycles Low level High level Guard ratio, db Minimum signal for just operate, ms Start of limit above just operate, db -28 150 60 0 355 -28 15075-6 355 -16 1506010 1005 -28 150 75 6 505 1322 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 iinoaiD xNnai oi. Fig. 8 — Simplified diagram of 1,600-cjele signaling circuit. IX-BAND SINGLE-FREQUENCY SIGNALING 1323 ward signal because the far end receiver at this time has a long operatetime. The signal receiver is connected in series with the receiving hraiichof the voice transmission path and is provided with a voice amplifier loprovide a l)lo(*king function so noises originating in the switciiing eciuip-ment or beyond will not interfere with operation of the sigiuding receiver,and to compensate for the signaling l)ri(lging loss. The receiving portion of the circuit is shown in the central and lowerportions of Fig. 8. The idle condition of the trunk is shown, tone is beingreceived, the r, rg and rf relays are operated and the band eliminationfilter is inserted in the receiving l)ranch to prevent signaling tone fromentering a connected circuit and interfering with signaling there. The signal cm-rents coming in from the line are passed through thesignal amp
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