Motorola Gm Series Detailed 6864115b62 A Manual

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Table of Contents
Chapter 1 MODEL CHART AND TECHNICAL SPECIFICATIONS
1.0 GM360 Model Chart............................................................................................. 1-1
2.0 Technical Specifications ...................................................................................... 1-1
Chapter 2 THEORY OF OPERATION
1.0 Introduction .......................................................................................................... 2-1
2.0 Low Band  Receiver...

iv
Chapter 4 Low Band PCB/SCHEMATICS/PARTS LISTS
1.0 Allocation of Schematics and Circuit Boards ....................................................... 4-1
1.1 Controller Circuits ................................................................................................ 4-1
2.0 LB1 25-60W PCB 8486206B06 / Schematics ..................................................... 4-3
2.1 LB1 25-60W PCB 8486206B06 Parts List ......................................................... 4-13
3.0 LB2 25-60W PCB...

Chapter 1
MODEL CHART AND TECHNICAL SPECIFICATIONS
1.0 GM360 Model Chart
2.0 Technical Specifications
Data is specified for +25°C unless otherwise stated.
GM Series Low Band 29-50 MHz
Model Description
MDM25BKF9AN5_EGM360 LB1, 29.0-36.0 MHz, 25-60W, 255 Ch
MDM25CKF9AN5_E GM360 LB2, 36.0-42.0 MHz, 25-60W, 255 Ch
MDM25DKF9AN5_EGM360 LB3, 42.0-50.0 MHz, 25-60W, 255 Ch
Item Description
XXXGCN6114_ Control Head, GM360
XIMUB6003_SField Replaceable Unit (Main Board) GM360
X IMUB6004_S Field Replaceable Unit...

1-2 MODEL CHART AND TECHNICAL SPECIFICATIONS
*Availability subject to the laws and regulations of individual countries.
Transmitter LB1 LB2 LB3
*Frequencies - Full BandsplitLB1 29.7-36.0 MHzLB2 36.0-42.0 MHzLB2 42.0-50.0 MHz
Channel Spacing12.5/20/25 kHz12.5/20/25 kHz12.5/20/25 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±5.0 ppm±5.0 ppm±5.0 ppm
Power 25-60W 25-60W 25-60W
Modulation Limiting±2.5 @ 12.5 kHz 
±4.0 @ 20 kHz
±5.0 @ 25 kHz±2.5 @ 12.5 kHz 
±4.0 @ 20 kHz
±5.0 @ 25 kHz±2.5 @ 12.5 kHz...

Chapter 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the LowBand circuits in the radio. For details 
of the theory of operation and trouble shooting for the the associated Controller circuits refer to the 
Controller Section of this manual. 

2-2THEORY OF OPERATION
2.0 Low Band Receiver
2.1 Receiver Front-End
The low band receiver is bandsplit into three ranges depending on radio model, covering frequencies 
from 29.7 to 36.0 MHz, 36.0 to 42.0 MHz, or 42.0 to 50.0 MHz. The circuitry of the three models is 
identical except for component value differences. The receiver consists of five major blocks: front-end 
bandpass filters and pre-amplifier, first mixer, high-IF and blanker switches, low-IF and receiver back-
end, and “Extender” (noise...

Low Band Receiver2-3
There are two 2-pole 10.7 MHz crystal filters in the high-IF section and two switched pairs of 
455 kHz ceramic filters in the low-IF section to provide the required adjacent channel selectivity. 
The second IF at 455 kHz is mixed, amplified and demodulated in the IF IC. The processing of the 
demodulated audio signal is performed by an audio processing IC located in the controller section.
2.2 Front-End Band-Pass Filters & Pre-Amplifier 
The received signal from the radio’s antenna...

2-4THEORY OF OPERATION
presented to the high-Q crystal filters FL1102 and FL1103, would cause ringing of the filter 
response, stretching an otherwise narrow impulse into a long and audible output waveform. 
Therefore, source follower stage Q1104 isolates the blanker switches from the crystal filters, 
providing a consistent source impedance via matching network L1106, L1107 and associated 
components. Q1104 has unity voltage gain in this configuration.
Crystal filters FL1102 and FL1103 are 2-pole, 10.7...

Low Band Transmitter Power Amplifier (PA) 25-60 W 2-5
3.0 Low Band Transmitter Power Amplifier (PA) 25-60 W
The radio’s 60 W PA is a three-stage amplifier used to amplify the output from the VCO to the radio 
transmit level. The line-up consists of three stages which utilize LDMOS technology. The first stage 
is pre-driver (U1401) that is controlled by pin 4 of PCIC (U1503) via Q1504 and Q1505 
(CNTLVLTG). It is followed by driver stage Q1401, and final stage utilizing two devices (Q1402 and 
Q1403)...

2-6THEORY OF OPERATION
antenna of the radio. The variation in the driver’s output power is limited by controlling its DC 
current. The driver’s DC current is monitored by measuring the voltage drop across current-sense 
resistors R1473-6, and this voltage is compared to a reference voltage on pin 6 of U1402-2. If the 
current through the sense resistors decreases, the circuit increases the bias voltage on the gate of 
Q1401 via Q1404. If the current increases, then the bias voltage decreases in order to...