Motorola PDR 3500, Базовое руководство по обслуживанию

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68P81093C75-O September 27, 2000 10-1
Functional Theory
of Operation
10
The following functional theory of operation provides an overview
of the station circuitry. For a more thorough functional description
of a particular module, refer to the appropriate section of the
Quantar User’s Guide (68P81095E05). Refer to the block diagram
in Figure 16. for the following functional theory of operation.
Transmitter Circuitry
Operation
Introduction
The Transmitter Circuitry consists of the following:
• Exciter Module
• Power Amplifier (PA) Module
These modules combine to produce the modulated, amplified RF
signal. The RF signal is transmitted via the station transmit antenna.
Exciter Module
Operation
The Exciter Module is a microprocessor-controlled module,
generating a modulated RF signal at the desired transmit frequency.
It sends this signal to the Power Amplifier for amplification. The
circuitry operates as follows:
1. The Synthesizer/Voltage-Control Oscillator (VCO) accepts
frequency programming data from the Station Control Module
(SCM) via the Serial Peripheral Interface (SPI) bus and
generates an RF carrier signal at the specified frequency.
The modulation audio signal from the SCM modulates the carrier,
resulting in a modulated RF signal at approxi13dBm. The
modulated signal is routed to the Power Amplifier.
2. The TX Power Control Circuitry accepts an output power detect
voltage from the Power Amplifier and compares this signal to a
reference voltage representing the desired output power.
Based on the comparison, a power control voltage is generated to
control the output power from the PA. This feedback and control
loop continually monitors the output power. It adjusts the control
voltage to maintain the proper output power from the PA.