Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

Technical Specifications1-3
Transmitter UHF
*Frequencies - Full BandsplitUHF 450-527 MHz
Channel Spacing12.5/20/25 kHz
Frequency Stability
(-30°C to +60°C, +25° Ref.)±2.0 ppm
Power 1-25W
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 Hz)+1 to -3 dB
Audio Distortion @1000Hz, 60%
Rated Maximum Deviation65 dB
Base...

1-4Technical Specifications
*Availability subject to the laws and regulations of individual countries.
Audio Response (300 - 3000Hz @ 20/25kHz)
(300 - 2550Hz @12.5kHz)+1 to -3 dB
Conducted Spurious Emission (ETS)-57 dBm 1 GHz
Receiver UHF 

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 the associated Controller circuits refer to the 
Controller Section of this manual.
2.0 UHF (450-527 MHz) Receiver
2.1 Receiver Front-End
The receiver is able to cover the UHF range from 450 to 527 MHz. It consists of four major blocks: 
front-end bandpass filters and pre-amplifier, first mixer,...

2-2UHF (450-527 MHz) Receiver
There are two 2-pole 44.85 MHz crystal filters in the high-IF section and 2 pairs of 455 kHz ceramic 
filters in the low-IF section to provide the required adjacent channel selectivity .The correct pair of 
ceramic filters for 12.5 or 25 kHz 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...

UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W 2-3
2.4 Low Intermediate Frequency (IF) and Receiver Back End
The 44.85 high 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 low IF signal at 455 kHz. The 2nd LO frequency is determined by crystal Y3101. The 
low IF signal is amplified and filtered by an external pair of 455 kHz ceramic filters FL3112,...

2-4 UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W
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 the op-amp U5402-1, pin 1. The control voltage 
simultaneously varies the bias of two FET stages within U5401. This biasing point determines the 
overall gain of U5401 and...

UHF (450-527 MHz) Transmitter Power Amplifier (PA) 25 W 2-5
3.4 Directional Coupler
The directional coupler is a microstrip printed circuit, which couples a small amount of the forward 
power delivered by Q5441. The coupled signal is rectified by D5451. The DC voltage is proportional 
to the RF output power and feeds the RFIN port of the PCIC (U5501 pin 1). The PCIC controls the 
gain of stages U5401 and Q5421 as necessary to hold this voltage constant, thus ensuring the 
forward power out of the radio...

2-6UHF (450-527 MHz) Frequency Synthesis
U5502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity 
of the transmitter driver and final devices, and provides a DC voltage to the PCIC (TEMP, pin 30) 
proportional to temperature. If the DC voltage produced exceeds the set threshold in the PCIC, the 
transmitter output power will be reduced so as to reduce the transmitter temperature.
4.0 UHF (450-527 MHz) Frequency Synthesis
The synthesizer subsystem consists of...

UHF (450-527 MHz) Frequency Synthesis2-7
4.2 Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U5201) consists of a pre-scaler, a programmable loop divider, 
control divider logic, a phase detector, a charge pump, an A/D converter for low frequency digital 
modulation, a balance attenuator to balance the high frequency analogue modulation and low 
frequency digital modulation, a 13V positive voltage multiplier, a serial interface for control, and 
finally a super filter for the regulated 5 volts....

2-8UHF (450-527 MHz) Frequency Synthesis
4.3 Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U5301), the TX 
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Figure 2-4 UHF VCO Block Diagram
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...