Tone Alarm Control
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
A Tone Alarm Control function is provided in a baseband modem without any loss of information on the transmit spectrum. The principle which has been chosen to perform the Tone Alarm Control function on a baseband coded signal is to transmit a low frequency tone and to detect it remotely. This tone is sent: when a power down is detected. - to initiate a remote self, or - to give a self test failure indication to the control modem. The tone chosen has been defined at 225 Hz which is the lowest frequency which can be transmitted on a baseband modem using DPSK (Differential Phase Shift Keying) coding, taking into account the usual line characteristics and the modem behavior at low frequencies.