Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

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Table of Contents
Section 1 Model Chart and Technical Specifications
1.0 GM338 Model Chart............................................................................................. 1-1
2.0 Technical Specifications ...................................................................................... 1-1
Section 2 Theory of Operation
1.0 Introduction .......................................................................................................... 2-1
2.0 UHF (450-520 MHz) Receiver...

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Section 4 UHF PCB/Schematics/Parts Lists
1.0 Allocation of Schematics and Circuit Boards ....................................................... 4-1
1.1 Controller Circuits ........................................................................................... 4-1
2.0 UHF Band 2 25-40W PCB / Schematics / Parts List ........................................... 4-3
UHF Band 2 (450-520 MHz) 40W 8486250Z02 Top Side ...................................... 4-3
UHF Band 2 (450-520 MHz) 40W 8486250Z02...

1-1
Section 1
MODEL CHART AND TECHNICAL SPECIFICATIONS
1.0 GM338 Model Chart
2.0 Technical Specifications
Data is specified for +25°C unless otherwise stated.
GM Series, UHF Band 2, 450-520 MHz
Model Description
AZM25SKF9AA5GM338 450-520 MHz 25-40W (LDMOS)
Item Description
XGCN6114_GM338 Control Head Direct Mount
X IMUE6019_ Tanapa WM 450-520 MHz 25-40W
XRAE4155_BNC 470-512 MHz, 1/4 Wave Roof Mount
X RAE4156_ BNC 470-494 MHz, 3.5 Gain Roof Mount
XRAE4157_BNC 494-512 MHz, 5dB Gain Roof Mount
X 6804112J06...

1-2Technical Specifications
*Availability subject to the laws and regulations of individual countries.Transmitter UHF
*Frequencies - Full BandsplitUHF 450-520 MHz
Channel Spacing12.5/20/25 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±2.0 ppm
Power 25-40W
Modulation Limiting
±2.5 @ 12.5 kHz 
±4.0 @ 20 kHz
±5.0 @ 25 kHz
FM Hum & Noise-40 dB @ 12.5kHz
-45 dB @ 20/25kHz
Conducted/Radiated Emission (ETS)-36 dBm 1 GHz
Adjacent Channel Power-60 dB @ 12.5 kHz
-70 dB @ 25 kHz
Audio Response (300 - 3000...

2-1
Section 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the UHF circuits in the radio. For details of 
the theory of operation and troubleshooting for the associated Controller circuits refer to the 
Controller Section of this manual.
2.0 UHF (450-520 MHz) Receiver
2.1 Receiver Front-End
The UHF receiver, shown in Figure 2-1, is able to cover the UHF range from 450 to 520 MHz. It 
consists of four major blocks: front-end bandpass filters and...

2-2UHF (450-520 MHz) Receiver
The two 2-pole 44.85 MHz crystal filters in the high-IF section and two pairs of 455 kHz ceramic 
filters in the low-IF section provide the required adjacent channel selectivity .The correct pair of 
ceramic filters for 12.5 or 25KHz channel spacing is selected via control line BWSELECT. 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...

UHF (450-520 MHz) Transmitter Power Amplifier (PA) 40W 2-3
2.4 Low Intermediate Frequency (IF) and Receiver Back End
The 44.85 MHz first IF signal from the second IF amplifier feeds the IF IC (U3101) at pin1. Within the 
IF IC the 44.85 MHz high IF signal mixes with the 44.395 MHz second local oscillator to produce a 
low IF signal of 455 kHz. The second LO frequency is determined by crystal Y3101. The second IF 
signal is amplified and filtered by an external pair of 455 kHz ceramic filters (FL3112 and...

2-4 UHF (450-520 MHz) Transmitter Power Amplifier (PA) 40W
3.1 First Power Controlled Stage
The first stage (U5401) is a 20dB gain integrated circuit containing two LDMOS FET amplifier 
stages. It amplifies the RF signal from the VCO (TXINJ). The output power of stage U5401 is 
controlled by a DC voltage applied to pin 1 from Q5473. The control voltage simultaneously varies 
the bias of two FET stages within U5401. This biasing point determines the overall gain of U5401 
and therefore its output drive...

UHF (450-520 MHz) Transmitter Power Amplifier (PA) 40W 2-5
3.5 Antenna Switch
The antenna switch consists of two PIN diodes, D5471 and D5472. In the receive mode, both 
diodes are off. Signals applied at the antenna jack J5401 are routed, via the harmonic filter, through 
network L5472, C5474 and C5475, to the receiver input. In the transmit mode, K9V1 turns on 
Q5471 which enables current sink Q5472, set to 96 mA by R5512 and VR5471. This completes a 
DC path from PASUPVLTG, through L5437, D5471, L5472,...

2-6UHF (450-520 MHz) Frequency Synthesis
4.0 UHF (450-520 MHz) Frequency Synthesis
The synthesizer subsystem shown in Figure 2-3, consists of the reference oscillator (Y5261 or 
Y5262), the Low Voltage Fractional-N synthesizer (LVFRAC-N, U5201), and the Voltage Controlled 
Oscillator (VCO).
4.1 Reference Oscillator
The reference oscillator (Y5262) contains a temperature compensated crystal oscillator with a 
frequency of 16.8 MHz. An Analog-to-Digital (A/D) converter internal to U5201 (LVFRAC-N) and...