A2 circuit - A2-Schaltung
In communications technology, an A2 circuit was a call station circuit with two telephones . A2 circuits date from the time when the Deutsche Bundespost still had a monopoly in the telecommunications sector. The parallel connection of two or more telephones to one subscriber line was not permitted; only one telephone was allowed to be active at a time. The A2 circuit was developed so that two telephones could still be connected. The two telephones were switched "one behind the other", whereby the hook switch of the first telephone was provided with additional contacts. These contacts switched when theHandset on the first telephone automatically from the second telephone (the A2 device). An incoming call was signaled on both telephones. A voice connection between the two devices could not be established.
Modes of operation
- If a call was being conducted on the first telephone, the second telephone was switched off.
- If a call was being conducted on the second telephone, the call was switched from the second to the first telephone by lifting the receiver on the first telephone. The second telephone was then switched off from the line. To prevent this from happening unintentionally, a type with a flag was used as the first telephone , which indicated an ongoing call on the second telephone. A first telephone with indicators had to be used when there was no line of sight between the two devices.
- A conversation could be passed from the first to the second telephone. To do this, the receiver of the second telephone had to be lifted while a conversation was in progress on the first telephone; by hanging up the receiver on the first telephone, the line was then switched through to the second telephone.
- A call could be passed from the second to the first telephone. To do this, the receiver of the first phone had to be lifted while a conversation was in progress on the second phone; the first telephone had the call immediately after lifting the receiver.
- The first telephone set had to have a modified hook switch and, if necessary, a flag: FeTAp 613 , FeTAp 614 , FeTAp 615 , FeTAp 616 or corresponding devices from the FeTAp 7 series.
- Any model available and approved at the time could be used as the second device; however, as a rule, a simple telephone was used in the basic configuration, e.g. B. FeTAp 611 , FeTAp 612 or corresponding devices from the FeTAp 7 series. The second set had to have an alarm clock line with which the ringing voltage was returned to the first set so that it would also ring. In the case of apparatus types of the FeTAp-7 series, the alarm clock line was interrupted when the receiver was removed and the inductance of the alarm clock was thus switched off from the a / b interface . This measure improved the transmission range the device circuit.