TM 11-7440-232-12/NAVELEX 0967-LP-275-5010
c. Data Carrier Alarm
(1) The data carrier alarm monitors transmitted and received data and carrier signals and provides fail-safe
individual alarm outputs to alarm equipment external to the digital data modem if trouble occurs in any of the monitored
signal paths.
Transmit Data Alarm monitors the output of the data amplifier in the transmitter, and provides an alarm 5
seconds after transmission stops.
Transmit Carrier Alarm monitors transmitter output as it is coupled to the transmission line and provides a
delay alarm output if the signal falls below a predetermined level.
Receive Data Alarm monitors the decoder output of the decoder error detector and provides an output if
more than 5 seconds elapse between two received data transitions.
Receive Carrier Alarm monitors carrier alarm output of the decoder error detector and provides an output,
two seconds after a loss of receive carrier is detected the data amplifier in the decoder error detector is
held in the mark condition until the alarm is cleared.
Alarm Cut Off Control, an alarm condition in any of the four sections of this unit can be canceled by
operating the ALARM CUT OFF switch to the CUT OFF position. When the switch is in the CUT OFF
position it clamps the alarm circuits in normal condition, regardless of any alarm signals at the input. In
the case of the receive carrier alarm, the switch will cancel the alarm output but not remove the mark hold
until the actual trouble is corrected.
(2) All alarms are arranged to actuate at a predetermined level and to reset again after returning to the
predetermined threshold level.
(3) Fail-safe feature will always provide an alarm output signal in the event any monitored signal path fails.
d. RF Oscillator
The RF oscillator is common to both transmit and receive branches of the Digital Data Modem MD-701(*)IUY. This
unit provides a stable 4.8 MHz sine wave timing signal to transmitter clock and to digital receiver clock.
e. Power Supply
The power supply is common to both transmit and receive branches of the Digital Data Modem MD-701(*)/UY.
This unit operates on a 115V 60 Hz (nominal) input line voltage and supplies regulated +12, +4, and -12 volts to the
modules. There are three potentiometers on the power supply module for adjusting the supply voltages to the modules.
On the front of the chassis is an on-off switch, indicator lamp, and ac line fuse; on the board are three fuses, one for each
supply voltage.
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