Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

1-1
Section 1
MODEL CHART AND TECHNICAL SPECIFICATIONS
1.0 GM338 Model Chart
GM Series, Low Band 
Model Description
AZM25BKF9AA5GM338 29.7-36.0 MHz 40-60W
AZM25CKF9AA5 GM338 36.0-42.0 MHz 40-60W
AZM25DKF9AA5GM338 42.0-50.0 MHz 40-60W
Item Description
X X X GCN6114_ Preferred Control Head Direct Mount
XIMUB6000_Tanapa WM 29.7-36.0 MHz 40-60W
X IMUB6001_ Tanapa WM 36.0-42.0 MHz 40-60W
XIMUB6002_Tanapa WM 42.0-50.0 MHz 40-60W
X RAB4002 Low Band 29.7-36.0 MHz, 
1/4 Wave Base Loaded
XRAB4003Low Band 36.0-42.0...

1-2Technical Specifications
2.0 Technical Specifications
Data is specified for +25°C unless otherwise stated.
General Specifications
Channel Capacity
GM338
128
Power Supply 13.2Vdc (10.8 - 15.6Vdc)
Dimensions:  H x W x D (mm)  Depth excluding knobsGM338
60mm x 179mm x 250mm (45 - 60W)
Weight GM338 2064 g
Sealing:Withstands rain testing per 
MIL STD 810 C/D /E and IP54
Shock and Vibration: Protection provided via impact
resistant housing exceeding MIL STD 
810-C/D /E
Dust, Salt & FogProtection provided...

Technical Specifications1-3
*Availability subject to the laws and regulations of individual countries.Transmitter Low Band
*Frequencies - Full Bandsplit
Low Band 1 29.7-36.0 MHz
Low Band 2 36.0-42.0 MHz
Low Band 3 42.0-50.0 MHz
Channel Spacing12.5/20/30 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±5 ppm
Power 40-60W 
Modulation Limiting±2.5 @ 12.5 kHz
±5.0 @ 20/30 kHz
FM Hum & Noise-40 dB @ 12.5kHz
-45 dB @ 20/30kHz
Conducted/Radiated Emission -26 dBm 70dB 
(1-25W model only)
Adjacent Channel...

1-4Technical Specifications
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2-1
Section 2
THEORY OF OPERATION
1.0 Introduction
This Chapter provides a detailed theory of operation for the Low Band 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 Low Band Receiver
2.1 Receiver Front-End
The low band receiver, shown in Figure 2-1, 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...

2-2Low Band Receiver
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 and Pre-Amplifier
The received signal from the radio’s antenna...

Low Band Receiver2-3
presented to the high-Q crystal filter FL1102, 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 filter F1102 is a module which consists of two 2-pole,...

2-4Transmitter Power Amplifier (PA) 60 W
AGC input pin 5 of U1601, reducing its gain and therefore the amount of noise pulses which are 
detected and processed.
3.0 Transmitter Power Amplifier (PA) 60 W
The radio’s 60W power amplifier (PA), shown in Figure 2-2, 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...

Transmitter Power Amplifier (PA) 60 W2-5
3.2 Driver Stage
The next stage is an LDMOS device (Q1401) providing a gain of 13dB. This device requires a 
positive gate bias and a quiescent current flow for proper operation. The voltage of the line 
MOSBIAS_1 is set during transmit mode by the PCIC pin 24, and fed to the gate of Q1401 via 
resistors R1402, R1447, R1449, R1458, R1459, and R1463. The bias voltage is tuned in the 
factory.
The circuitry associated with U1402-2 and Q1404 limits the variation in...

2-6Transmitter Power Amplifier (PA) 60 W
3.6 Power Control
The transmitter uses the Power Control IC (PCIC, U1503) to control the power output of the radio. A 
differential DC amplifier U1502-1 compares the voltage drop across current-measuring resistor 
R1409, which is proportional to the transmitter final stage DC current, with the voltage drop across 
resistors R1508 and R1535, which is proportional to the current through transistor Q1503. This 
transistor is controlled by the output of the...