3.1.3
Frequency Bands
The Modem Module covers the following bands with unique models:
• VHF
• UHF
3.2
Receiver Subsystem
3.2.1
Description
The Modem Module includes the receiver circuitry for the station. A cable connects the board
connector to a BNC connector located on the rear panel of the repeater. See Figure 8: Modem Module
Connector Locations on page 48 for the location of this connector. The receiver section performs
highly-selective bandpass filtering and dual down-conversion of the desired RF signal. A custom
Receiver IC then performs an analog-to-digital conversion of the desired received signal and outputs
the digitized signal to the controller section via a serial synchronous interface. Included in the receiver
section is:
• Frequency Synthesizer Circuitry – Consists of a phase-locked loop and Voltage-Controlled
Oscillator (VCO), generates the first LO injection signal.
• Varactor-tuned Preselector Filter(s) – Provides bandpass filtering of the station Receiver RF input.
• Receiver Front End Circuitry – Performs filtering, amplification, and the first down conversion of the
Receiver RF signal.
• Receiver-specific piece of transceiver IC Circuitry – Consists of receiver-specific parts of a
transceiver IC which performs the second down conversion, filtering, amplification, and analog-to-
digital conversion of the receive signal.
• Analog to Digital Converter (ADC) Circuitry – Converts analog Receiver status signals to digital
format for transfer to the controller circuitry located on the Modem Module.
3.2.2
Specifications
Table 11: Specifications of Receiver Subsystem
Parameter Specifications
VHF UHF
Frequency Bands 136–174 MHz 400–470 MHz
Selectivity 25 kHz/12.5 kHz (TIA603D) 83 dB/55 dB 80 dB/55 dB
Selectivity 25 kHz/12.5 kHz (TIA603) 83 dB/68 dB 80 dB/68 dB
Selectivity 25 kHz/12.5 kHz (ETSI) 70 dB/63 dB
Sensitivity (12 dB SINAD) 0.22 uV
Sensitivity (5% BER) 0.22 uV
Intermodulation Rejection (TIA603D) 82 dB
Intermodulation Rejection (ETSI) 73 dB
Table continued…
Chapter 3: SLR 5000 Series Modem
Motorola Solutions Confidential
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