Can anyone provide detailed knowledge of ordinary telephone lines?

The two wires of an ordinary telephone line have a DC feed added to them with positive and negative, but when connected to an ordinary telephone set, there is no need to differentiate and the two wires can be connected at random. The polarity conversion circuit (4 diodes) inside the telephone ensures that the telephone gets the correct polarity voltage and works properly.

Ordinary telephone line function: Simply put, it is to feed the electricity, transmission signaling signals and language signals. Signaling signals include: ringing signals, dial tone, DTMF, and so on.

Feeder: supply the telephone work of electrical energy. China's telephone line feed voltage 48 V. Ordinary telephones rely on the switchboard feed to work.

Ringing signal: 60-80V20Hz AC signal

Dual Tone MultiFrequency is DTMF (Dual Tone MultiFrequency), DTMF signal is composed of 8 frequencies two by two combination. The 8 frequencies are divided into two groups: the low frequency group and the high frequency group. The four frequencies of the low frequency group are 697Hz, 770Hz, 852Hz and 941Hz; the four frequencies of the high frequency group are 1209Hz, 1336Hz, 1477Hz and 1336Hz in order. signal transmission. In the dialing signal applied to the telephone, according to the national telecommunication standard, the signal duration and interval time are not less than 40 m s, and the frequency deviation is not more than ± 1.5 %. 5 %.

Ordinary telephone lines, telephone principle here the limitations of space, can not be detailed, if you are interested, we recommend that you find a "principle of the telephone" to see, which has a detailed description.