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. This capability requires installation of third

party, Internet Protocol (IP) compliant DES encryption and decryption software on the system.

The standard IP circuit board contains ten (10) sections defined below.

These added sections will be discussed in Section 4 of this document.

Input/Output Circuitry associated with the radio’s DB25 data connector providing all the

RS232 data and handshake functions, including the necessary level

changes.

Microcontroller Manages the operation of the radio loading the selected transmit/receive

frequencies into the injection synthesizer, controls the operation of the

modem, and determines which receiver provides a better signal from a

given transmission. Also provides transmit time-out protection in the event

a fault causes the radio to halt in the transmit mode.

Transmit Processing Circuitry that amplifies the analog audio signal from the modem and uses it

to modulate the voltage controlled oscillator (VCO) and 10 MHz reference

oscillator in the injection synthesizer section. Modulating the VCO and

reference oscillator simultaneously results in a higher quality FM signal.

Modem Converts parallel data into an analog audio waveform for transmission and

analog audio from the receiver to serial data. Serial data appears on the

radio’s RS232 port, which connects a Mobile Data Computer (MDC) or a

Voice Interface Unit (VIU).

Input /

Output

Micro-

Controller

Injection

Synthesizer

Transmitter

Transmit

Processing

Baseband

Routing

Receiver 1

Receiver 2 Modem