Objects to be measured - Analogue telecommunication devices

Notation:

• E - earphone
• MIC - microphone
• H - hybrid - bridge connection for separating signals of earphone and microphone
• BN - Balanced Network - used to balance a hybrid as a bridge connection
• RID - Ring, signal of calling
• DIC - Dialer - keypad (DTMF)
• SW - A switch operated by the receiver. In case of a hung-up receiver the ring is the one, that connects to the line, and in case of a picked up receiver the hybrid.
• line - Analogue device line

• Full duplex signal transmission capability on two wires. Separation of directions happens in the device and the exchange with hybrid circuits (H). Hybrid is an eight-pole, a bridge connection, and in case, when it is balanced, the opposite switch pairs (MIC-E, line-BN) cannot see each other.A balancing circuit (BN) provides this balance.

• Remote feeding of the subscriber device. Remote feeding is provided by the direct current (DC) power source (a feeding bridge) in the exchange.

• Signal transmission capability. Signal is a data exchange serving for setting up and control of line switched connection. These signals could be:
  • Direct current signals (close/break of the remote feeding loop with the SW switch, which can be operated by picking up/hanging up of the receiver.)

  • Signals under the speech band (300-3400 Hz) (ringing of 25 Hz). This signal is sent by the exchange to the device

  • Signals falling to the speech band. (Sending dialing numbers, answering signals of the exchange: dialing sound, ringing echo...). Sending of numeric characters to the exchange happens with signals coded with sound frequencies. A signal consisting of the total amount of two sinusoid signals corresponds to each of the numeric characters, according to the following table:

    Frequencies of the DTMF (Dual Tone MultiFrequency) signals:

    Hz	1209	1336	1477	1633
    697	1	2	3	A
    770	4	5	6	B
    852	7	8	9	C
    941	*	0	#	D

  Signal level of the DTMF: 800 Hz -4dBm0 1600 Hz -7dBm0