Motorola PM1200, Basic Service Manual

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Chapter 3 Basic Theory of Operation
3.1 Introduction
The PM1200 radio combines the controller and RF sections into a single board and contains the
following modules:
• Daughtercard
• RX VCO module
• TX VCO module
It is important to correctly identify the malfunctioning region before replacing expensive modules. To
assist with radio repair, descriptions of the sections contained on the PM1200 uniboard are listed
below.
3.2 General Overview
The PM1200 radios are wideband, synthesized, fixed-tuned radios and are available with the
following frequency bands:
• VHF Low-Band A (29.7 – 37.0 MHz)
• VHF Low-Band B (37.0 – 50.0 MHz)
The PM1200 radios contain the following assemblies and sections:
• Control Head Assembly — The control head assembly contains the DISPLAY-UNIT, KEY-UNT,
VR-UNIT, and PANEL-INTERFACE-UNIT to communicate with the RF deck.
For the remote mount configuration, the control head assembly is attached to the
RF-INTERFACE -UNIT via a flex. Each unit is used to communicate with the RF deck.
• RF-INTERFACE-UNIT (Remote mount only) — Provides interface to remote control head
assembly. Connects to the RF deck via a flex.
• Power Amplifier (PA) section — contains the antenna switch, directional coupler/ detector, and
amplifier(s).
• Front-End Receiver section — contains the preselector, low-noise amplifier (LNA), and mixer.
• IF section — contains the receiver intermediate-frequency (IF) amplifier/filter and the digital
receiver back-end integrated circuit (IC).
• Frequency Generation section — contains the synthesizer, voltage-controlled oscillators
(VCOs), reference oscillator, and receive and transmit buffers.
• Controller section — contains the following elements:
– Voltage regulators and data communication circuitry (Accessory Port)
– Daughter card module (MDC-1200, Quik-Call II Decoder)
– Modulation D/A conversion circuitry
– CODEC audio circuitry
– TX power-control circuitry
– Emergency circuitry
– Accessory Interface Boards (Connector-Unit)
– DC power-in plug