. The Bell System technical journal . 20 30 40 TIME IN MILLISECONDS TRANSIENT VOLTAGE AT RECEIVING END (+7TL) Fig. 6 — Example of transient voltages generated by relay operation. 1320 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954. IN-BAXD SIXGLE-FREQUEXCY SIGNALING 1321 Iwlow normal and yet permit release in the presence of as much as 50 dbaof thermal noise at zero transmission level. SPECIFIC DESIGNS The two signaling systems 1,600 and 2,GOO cycles, are basically similarin principle. However, as can be seen by reference to Fig. 5, a simpleguard type receiver having a frequency of 1,600 cyc
. The Bell System technical journal . 20 30 40 TIME IN MILLISECONDS TRANSIENT VOLTAGE AT RECEIVING END (+7TL) Fig. 6 — Example of transient voltages generated by relay operation. 1320 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954. IN-BAXD SIXGLE-FREQUEXCY SIGNALING 1321 Iwlow normal and yet permit release in the presence of as much as 50 dbaof thermal noise at zero transmission level. SPECIFIC DESIGNS The two signaling systems 1,600 and 2,GOO cycles, are basically similarin principle. However, as can be seen by reference to Fig. 5, a simpleguard type receiver having a frequency of 1,600 cycles would have toomany signal imitations. To ONercome this the guard ratio during thetalking condition was increased from 6 to 10 db, the minimum signalinterval to just cause a response was increased to 100 milliseconds duringthe talking condition and the sensitivity was decreased to —16 a result fairly complicated timing and switching circuits are neededto assure that both transmitting and receiving circuits have the rightcondition at the right time. Table V gi^es a sununary of the principal design parameters of thetwo systems. DESCRIPTION OF 1,600-CYCLE DESIGN A front view of the 1,600-cycle main unit is shown in F
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