Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

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
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 GM338...

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...

Transmitter Power Amplifier (PA) 40W2-3
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 FL3114) for 
20/25...

2-4Transmitter Power Amplifier (PA) 40W
3.1 Power Controlled Stage
The first stage (U5401) amplifies the RF signal from the VCO (TXINJ) and controls the output power 
of the PA. The output power of the transistor U5401 is controlled by a voltage control line feed from 
the PCIC (U5501, pin 4). 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 level to 
Q5421, which in turn controls the...

Transmitter Power Amplifier (PA) 40W2-5
3.6 Antenna Switch
The antenna switch utilizes the existing dc feed (A+) to the last stage device (Q5441). Basic 
operation is to have both PIN diodes (D5471 and D5472) turned on during key-up by forward 
biasing them.   This is achieved by pulling down the voltage at the cathode end of D5472 to around 
11.8V (0.7V drop across each diode). The current through the diodes needs to be set around 80mA 
to fully open the transmit path through resistor R5496. Q5472 is a...

2-6Frequency Synthesis
4.0 Frequency Synthesis
The synthesizer, shown in Figure 2-3, consists of a reference oscillator (Y5261 or Y5262), low 
voltage LVFRAC-N synthesizer (U5201), and a 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 
controlled by the µP via serial interface (SRL) sets the voltage at the...

Frequency Synthesis2-7
Figure 2-3 UHF Synthesizer Block Diagram
Output LOCK (U5201-4) provides information about the lock status of the synthesizer loop. A high 
level at this output indicates a stable loop. IC U5201 provides the 16.8 MHz reference frequency at 
pin 19.
The serial interface (SRL) is connected to the µP via data line DATA (U5201-7), clock line CLK 
(U5201-8), and chip enable line CSX (U5201-9).
DATA
CLK
CEX
MODIN
VCC, DC5V
XTAL1
XTAL2
WARP
PREIN
VCP
REFERENCE
OSCILLATOR
 VOLTAGE...

2-8Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The voltage controlled oscillator (VCO), shown in Figure 2-4, consists of a VCO buffer IC (VCOBIC, 
U5301), TX and RX tank circuits, external RX buffer stages, and modulation circuits.
The VCOBIC together with Fractional-N synthesizer (U5201) generates the required frequencies in 
both transmit and receive modes. The TRB line (U5301, pin 19) determines which tank circuits and 
internal buffers are to be enabled. A high level on TRB enables TX...