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Page Title:
CHAPTER 4 ORGANIZATIONAL MAINTENANCE PRINCIPLES OF OPERATION |
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  TM 11-7440-232-12/NAVELEX 0967-LP-275-5010
CHAPTER 4
ORGANIZATIONAL MAINTENANCE
PRINCIPLES OF OPERATION
Section I. BLOCK DIAGRAM DESCRIPTION
4-1. GENERAL
The Digital Data Modem MD-701(*)/UY is a modulator-demodulator used for transmitting and receiving serialized
digital data at speeds of 600, 1200, and 2400 bps over a standard 3kHz voice channel. It has a transmit branch, which
consists of two modules and a RF oscillator, and a receive branch, which consists of five modules and the same RF
oscillator. A power supply is common to both branches. The MD-701A/UY and MD701B/UY have a data carrier alarm
module which provides a fail-safe alarm output if the modem malfunctions.
Transmitter
嫂ccepts serial-by-bit binary data at specified bps rate.
感roduces synchronous frequency modulated output.
愚atching transformer couples transmitter output to vf path.
惹upplies square wave output to transmitter clock at specified bps rate.
感rovides test pattern generator for checking modem operation.
Transmitter Clock
愛eceives stable 4.8 MHz sine wave from RF oscillator.
感rovides 2400 Hz square wave timing signal to transmitter.
感roduces secondary timing source for synchronizing related data equipment.
Receiver Line Filter
愚atching transformer couples input signal to low pass filter.
微ow pass filter amplifies signal and applies it to band pass filter.
媲and pass filter initially shapes duobinary signal.
Adjustable Equalizer
幌qualizes any delay and amplitude distortion that occurs in receive signal path.
Limiter Discriminator
愛eceives binary or duobinary encoded frequency modulated signals.
嵩onverts signals into analog form.
嵩ontrols a path between the output transmitter line filter and the limiter
discriminator when REC MODE switch is placed in BACK-TO-BACK mode for
checking modem operation.
感rovides local testing of some receive circuits.
Decoder Error Detector
愛egenerates signals from limiter discriminator to a serial-by-bit NRZ form.
愚onitors the received data pattern and provides alarm signal when errors are
detected.
愚onitors the received carrier signal level and provides alarm signal if level
decreases below a preset level.
感rovides an error visual indication by means of an ERRORS indicator lamp.
4-1
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