Owners of paired phones. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony
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Many radio amateurs who have two telephones installed at home know the situation when they speak on one phone, and on the second, without making sure that the line is free, they start dialing, which creates inconvenience in the form of clicks (during pulse dialing) or tonal sound signals that interfere with conversation.
To eliminate this, I suggest installing one of the signaling devices described below or a blocker in telephone sets or telephone sockets, which allows you to simultaneously get rid of eavesdropping on a conversation and "ringing" the phone while dialing on the second telephone set (Fig. 3).
The first signaling device is included in the break of the telephone line and, by lighting up the LED, indicates that the handset on the device is off-hook (Fig. 1).
The second indicator, on the contrary, when the LED is on, indicates that the line is free. It is connected in parallel with the telephone line (Fig. 2).
Capacitors C1, C2 (Fig. 3) are chosen such that the frequency of the oscillatory circuit formed by the relay winding and the capacitor does not coincide with the frequency of the ringing signal from the station (30 ... 60 Hz) and the beep frequency (about 500 Hz), and when tone dialing - also with the frequency of the tone signal. It is better if the frequency of this oscillatory circuit is higher than 10 kHz.
As relays K1 and K2, any low-power relays with a winding resistance of up to 200 ohms and a trip current of not more than 15 mA are suitable.
When a call signal is received from the PBX, with the blocker installed, both phones will ring. The one on which they pick up the phone first will turn on.
Author: A.Filipovich, Dzerzhinsk
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