SECTION 1: THEORY OF OPERATION
369548.DOC
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Modems
Convert data into an analog audio waveform for transmission and
analog audio from the receiver to serial data interface. There is one
(1) modem that is dedicated to the transmit operation and two (2)
modems dedicated to the receive operation. The modem dedicated
to the transmit supports a 115.2 KBPS data transmission rate on the
serial port, SLIP protocol, and 19.2 KBPS and 32 KPBS over-the-air
data transmission rate. Provides Forward Error Correction (FEC)
and Error Detection (CRC), bit interleaving for more robust data
communications, and third generation collision detection and
correction capabilities.
Diversity
Reception
Circuitry selects one of three (3) diversity receiver audio outputs for
processing by the modem by comparing the Received Signal
Strength Indication (RSSI) output from each receiver. Audio from the
receiver with the highest RSSI value is passed to the modems.
RX Injection
The Injection Synthesizer board provides a highly stable local
oscillator signal for the three (3) receivers. This displays a serial
data input/output interface, synthesizer, and VCO.
Transmitter
Consists of an exciter and a power amplifier module covering various
frequency bands in segments. A different power amplifier module is
required for each segment. The transmitter power control is included
with the power supply circuitry on the same board.
Receiver 1/Receiver 2/
Uses three (3) discrete receivers tuned to the same frequency.
Receiver 3
The three (3) receivers are required to support
IP
MobileNet’s base
station Diversity Reception System (DRS).
NOTE:
Some installations use only two (2) receivers.
The receivers are double-conversion superhetrodynes with an
Intermediate Frequency (IF) of 45 MHz. Each receiver consist of
bandpass filters, RF amplifiers, a mixer, 45 MHz crystal filter, and a
one-chip IF system. The injection synthesizer provides the first local
oscillator signal and outputs from each receiver including RSSI and
analog audio for Diversity Reception.
Power Supply
Power supply circuitry derives the various operating voltages
required by the base station. Fixed voltage regulators are employed
through the base station for this purpose.
