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 VHF (136-174 MHz)...

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Section 4 VHF PCB/Schematics/Parts List
1.0 Allocation of Schematics and Circuit Boards ....................................................... 4-1
1.1 Controller Circuits ........................................................................................... 4-1
2.0 VHF 25-45W PCB / Schematics / Parts List ........................................................ 4-3
VHF (136-174 MHz) 25-45W 8486140B13 Top Side ............................................. 4-3
VHF (136-174 MHz) 25-45W 8486140B13...

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, VHF 136-174 MHz
Model Description
AZM25KKF9AA5GM338 136-174 MHz 25-45W
Item Description
XGCN6114_GM338 Control Head Direct Mount
X IMUD6011_ Tanapa WM 136-174 MHz 25-45W
XRAD4198_BNC 136-144 MHz, 1/4 Wave Roof Mount
X RAD4199_ BNC 146-150.8 MHz, 1/4 Wave Roof Mount
XRAD4200_BNC 150.8-162 MHz, 1/4 Wave Roof Mount
X RAD4201_ BNC 162-174...

1-2Technical Specifications
*Availability subject to the laws and regulations of individual countries.Transmitter VHF
*Frequencies - Full BandsplitVHF 136-174 MHz
Channel Spacing12.5/20/25 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±2.5 ppm
Power 25-45W 
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 -...

2-1
Section 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the VHF circuits in the radio. For details of 
the theory of operation and troubleshooting for the the associated Controller circuits refer to the 
Controller Section of this manual.
2.0 VHF (136-174 MHz) Receiver
2.1 Receiver Front-End
The receiver is able to cover the VHF range from 136 to 174 MHz. It consists of four major blocks: 
front-end bandpass filters and pre-amplifier, first mixer, 1st...

2-2VHF (136-174 MHz) Receiver
There are two 2-pole 44.85 MHz crystal filters in the 1st IF section and 2 pairs of 455 kHz ceramic 
filters in the 2nd IF section to 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...

Transmitter Power Amplifier (PA) 45 W2-3
2.4 2nd Intermediate Frequency (IF) and Receiver Back End
The 44.85 MHz 1st 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 (2nd LO) to 
produce the 2nd IF signal at 455 kHz. The 2nd LO frequency is determined by crystal Y3101. The 
2nd IF signal is amplified and filtered by an external pair of 455 kHz ceramic filters FL3112, FL3114 
for 20/25...

2-4Transmitter Power Amplifier (PA) 45 W
3.1 Power Controlled Stage
The first stage (U3401) is a 20 dB gain integrated circuit containing two LDMOS FET amplifier 
stages. It amplifies the RF signal from the VCO (TXINJ). The output power of stage U3401 is 
controlled by a dc voltage applied to pin 1 from the power control circuit (U3501 pin 4, with 
transistors Q3501 and Q3502 providing current gain and level-shifting). The control voltage 
simultaneously varies the bias of two FET stages within U3401....

Transmitter Power Amplifier (PA) 45 W2-5
3.6 Antenna Switch
The antenna switch consists of two PIN diodes, D3471 and D3472. In the receive mode, both diodes 
are off. Signals applied at the antenna jack J3401 are routed, via the harmonic filter, through 
network L3472, C3474 and C3475, to the receiver input. In the transmit mode, the keyed 9 volts 
turns on Q3471 which enables current sink Q3472, set to 96 mA by R3473 and VR3471. This 
completes a dc path from PASUPVLTG, through L3473, D3471, L3477,...

2-6Frequency Synthesis
4.0 Frequency Synthesis
The frequency synthesizer subsystem consists of the reference oscillator (Y3261 or Y3262), the 
Low Voltage Fractional-N synthesizer (LVFRAC-N, U3201), and the voltage-controlled oscillators 
and buffer amplifiers (U3301, Q3301-2 and associated circuits).
4.1 Reference Oscillator
The reference oscillator (Y3262) contains a temperature compensated crystal oscillator with a 
frequency of 16.8 MHz. An analog-to-digital (A/D) converter internal to U3201...