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Blocker, developed by Merkulov [1], which is well established in the work, I propose adding led lights (VD1 and VD2). Now subscribers parallel phones see if the line is and if they do not interfere with each other.
Another advantage of the proposed improvements is that when dialing no Pozvoni" on the other phone.
Literature
1. Merkulov A. Telephone quasivelocities. - Ham, 1994.N9.C.26.
Author: A. White, Donetsk region, Artemovsk; Publication: N. Bolshakov, rf.atnn.ru