Motorola Professional GP680 Informations sur les services - Page 11

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1.0

This Chapter provides a detailed theory of operation for the VHF circuits in the radio. For details of

the theory of operation and trouble shooting for the the associated Controller circuits refer to the

Controller Section of this manual.

2.0

(Refer to Figure 2-1 and the VHF Transmitter schematic diagram)

The VHF transmitter consists of the following basic circuits:

Power amplifier (PA).

Antenna switch/harmonic filter.

Antenna matching network.

Power Control Integrated Circuit (PCIC).

From

VCO

2.1

The power amplifier consists of two devices:

1. LDMOS driver IC (U3501)

2. LDMOS PA (Q3501)

The LDMOS driver IC contains two stages of amplification with a supply voltage of 7.3V.

This RF power amplifier is capable of supplying an output power of 0.3W (pin 6 and 7) with an input

signal of 2mW (3dBm) (pin16). The current drain is typically around 130mA while operating in the

frequency range of 136-174MHz.

PCIC

Vcontrol

Power

Amplifier

Driver

Figure 2-1 VHF Transmitter Block Diagram.

THEORY OF OPERATION

Vcontrol

PA Final

Antenna Switch/

Stage

Harmonic Filter

Chapter 2

Antenna

Matching

Network