User Manual

SECTION 1: THEORY OF OPERATION
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General Block Diagram
General Block Diagram Definitions
For increased data security, the modem supports the U.S. Government developed Digital Encryption
Standard (DES) data encryption and decryption protocols.
The standard Base Station Data Radio circuit board contains eight (8) sections defined below:
Input/Output Circuitry associated with the base station’s DB25 data connector
providing all of the RS232 data and handshake functions, including
the necessary RS232 to logic level changes.
System Controller Manages the operation of the base station loading selected transmit/
receive frequencies into the injection synthesizer, controls the
operation of the modem and provides transmit timeout protection in
the event a fault causes the radio to become stuck in the transmit
mode.
Includes memory for storage of base station operating parameters.
Electrically erasable programmable read only memory (EEPROM) is
used to store parameters entered by the technician such as channel
numbers and RX/TX frequencies. This information is retained after
power is removed from the base station.
Transmit Processing Circuitry, which amplifies the analog audio signal from the modem
and uses it to modulate a voltage-controlled oscillator (VCO) and
reference oscillator in the transmitter synthesizer section.
Modulating the VCO and reference oscillator simultaneously results
in a higher quality FM signal.