. The Bell System technical journal . h is usually nearthe upper frequency point at which the overall circuit loss begins tobe appreciably greater than the loss at 1000 cycles. Figure 4 shows a f^ r f ~^ 1200 1600 2000 2400 2800 FREQUENCY IN CYCLES PER SECOND 3600 4000 Fig. 4—Singing frequency in 22 tests on 46 19-gauge B & H-88-50 two-wire cable circuits. cumulative plot of the singing frequencies during 22 tests ^ on 4619-gauge B & H-88-50 two-wire cable circuits. It may be seen that ^ A 22 test is a singing test made by increasing the gain of a normal workingrepeater in a two-wire circuit u
. The Bell System technical journal . h is usually nearthe upper frequency point at which the overall circuit loss begins tobe appreciably greater than the loss at 1000 cycles. Figure 4 shows a f^ r f ~^ 1200 1600 2000 2400 2800 FREQUENCY IN CYCLES PER SECOND 3600 4000 Fig. 4—Singing frequency in 22 tests on 46 19-gauge B & H-88-50 two-wire cable circuits. cumulative plot of the singing frequencies during 22 tests ^ on 4619-gauge B & H-88-50 two-wire cable circuits. It may be seen that ^ A 22 test is a singing test made by increasing the gain of a normal workingrepeater in a two-wire circuit until singing begins. SINGING ON TWO-WIRE CABLE CIRCUITS 607 over 80 per cent of these frequencies were between 2200 and 3100cycles, while the nominal transmitted band on these facilities is from250 to 3000 cycles. Consider the case of the return loss of one circuit in a group of cablesections. A typical curve of the passive return loss of such a circuitis shown on Fig. 5. It will be seen that it consists of a set of wabbles. 1400 1600 1800 2000 FREQUENCY IN CYCLES PER SECOND Fig. 5—Typical return-loss-frequency characteristic of a 19-gauge H- circuit repeater section. -50 side around a general trend line. When a measurement of return loss ismade at a single pre-selected value, the return loss obtained is deter-mined by what may be considered as two components, (1) the generalquality of the repeater section as determined by the trend line, and(2) the particular part of the wabble on which the particular fre-quency measurement happens to fall (, the bottom or top, or inbetween point of a given wabble ). In measuring the returnlosses of a large group of lines at, say, 2900 cycles, the lower values ofreturn loss will tend to be those which happened to be measured atthe bottom of a wabble. The higher the return loss of a given 608 BELL SYSTEM TECHNICAL JOURNAL circuit, the more chance there is that the return loss of that Hnehappened to be measured at the top of a wabble. Wh
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
