The telephone answering machine's function is to transmit a message to a subscriber who calls an unattended telephone. With most types, the answering machine will record any message the caller wishes to leave. The message that is pre-recorded, and the callers messages are stored on magnetic cassette tape.
When ringing, a telephone is energised by an alternating current (AC) received from the exchange on the ring line. If an answering machine is fitted to the telephone then the AC current will be detected and the line answered automatically by the machine after a predetermined period.
There are machines which only transmit messages, rather than receive them. The message is pre-recorded on a closed loop of tape and is recorded with conventional methods. The system includes an erase head to eliminate any previous recorded message on the loop. When the answering machine is activated the message is replayed. It has the additional function to be able to stop automatically after the message has been through one cycle. Those machines with short messages (approximately 15 to 30 seconds) usually permit two cycles of the tape. In other words, it plays the message twice before stopping.
