. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. 590 BELL SYSTEM TECHNICAL JOURNAL Frequency Directions. The importance of the use of a separate frequency for each direction of transmission may be considered by reference to Figure 14. If there are two paralleHng telephone circuits. Level ot Input to Carrier Aooarstus Leve^at Input to Carrier Apparatus Figure 14—Diagram illustrating occurrence of near-end crosstalk between carrier systems employing the same frequency for opposite directions of transmission employing f
. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. 590 BELL SYSTEM TECHNICAL JOURNAL Frequency Directions. The importance of the use of a separate frequency for each direction of transmission may be considered by reference to Figure 14. If there are two paralleHng telephone circuits. Level ot Input to Carrier Aooarstus Leve^at Input to Carrier Apparatus Figure 14—Diagram illustrating occurrence of near-end crosstalk between carrier systems employing the same frequency for opposite directions of transmission employing frequencies (/i) in the same range, and if there exists between the two circuits a certain amount of crosstalk, when there is a talker at the terminal of one system (No. 1) and a listener at the same terminal of the other system (No. 2), then the speech from the talker at the high level will enter directly into the sensitive receiving circuit of the listener. This is commonly called "near-end" crosstalk. In the case of a carrier circuit, the transmitting terminal would involve a certain amount of amplification. The receiving circuit would likewise, so that the net effect would be that the crosstalk between the two circuits would be amplified by the combined amount of gain or amplification present in the sending and receiving circuits. In telephone parlance it would be stated that this is a situation in which substantial level differences exist between the two circuits. On the other hand, in the case of two adjacent carrier systems employing the same frequencies for the same direction of transmission, a crosstalk situation involving only "far-end" crosstalk would exist, as illustrated in Figure 15. This assumes that near-end crosstalk by reflection as discussed later has been eliminated. In this case the talker and the listener would be situated at opposite terminals of the paralleling circuits and the crosstalk, while being amplified like the near-end cross
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