Telegraph engineering : a manual for practicing telegraph engineers and engineering students (1922)
Hausmann, Erich, 1886- · New York : D. Van Nostrand Company · leaf 313
smallto these ringing currents, resulting in chattering of therelay armatures. Instead, calling is accomplished bymeans of weak high-frequency currents (about 300 cycles)over the lines which actuate suitable relays that controlthe operation of local low-frequency ringing devices. Phantom Circuits…
Telegraph
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