CIRCUIT DESCRIPTION

SECTION 3 CIRCUIT DESCRIPTION

3.1 GENERAL TRANSCEIVER DESCRIPTION

3.1.1 INTRODUCTION

NOTE: A block diagram of the audio and data processing circuitry on the audio/logic board is located in Figure 3-3,and block diagrams of the RF boards are located in Figures 3-4and 3-7.

The 9800-series transceivers contain the PC board assemblies listed below. Components are mounted on only the top side of all boards. Therefore, most components can be changed without removing the board from the chassis.

Audio/Logic - Control logic and audio processing.

Display - This board contains the LCD display and controller and interface microcontroller.

Interface - This small board provides the electrical connections between the display and audio/logic boards, and contains the front panel rotary controls and microphone jack.

RF Board - Receiver, synthesizer, and exciter.

PA Board - Transmitter power amplifier.

General descriptions of the main sections such as the receiver, synthesizer, and exciter follow, and detailed descriptions are located in later sections.

3.1.2 CIRCUIT PROTECTION (FUSES)

Circuit protection is provided by a 15-ampere inline power cable fuse, 4-ampere fuse F500 on the RF board (in the unswitched battery supply line from the PA board), and by voltage regulators which automatically limit current. The 15-ampere power cable fuse protects the power amplifier module and final stages on the power amplifier board, and the 4-ampere fuse protects the remainder of the circuitry. In addition, there are two fuses on the audio/logic board. One fuse (F100, 2A) limits the current of the switched battery supply fed to accessory connector J101, the microphone jack, and also the display board. The other fuse

(F300, 0.6A) limits the current of the 8-volt supply fed to modem jack J301. For information on power distribution and switching, refer to Section 3.2.

3.1.3 SYNTHESIZER

The synthesizer output signal is the transmit frequency in the transmit mode and the receive first injection frequency in the receive mode. The synthesizer also provides the receiver second injection signal by tripling the TCXO frequency.

Channels are selected by programming the main divider in synthesizer integrated circuit U804 to divide by a certain number. This programming is provided by microcontroller U101 on the audio/logic board. The minimum frequency resolution is 6.25 or 10 kHz. The frequency stability of the synthesizer is determined by the stability of TCXO U806 (Temperature Compensated Crystal Oscillator). The TCXO has a frequency stability of ± 2.0 PPM (UHF) or ± 1.5 PPM (800/900 MHz) from –22° to +140° F (–30 to +60° C).

3.1.4 AUDIO/LOGIC BOARD

Microcontroller U101 on the audio/logic board provides transceiver control functions including synthesizer programming, system and group scan, data encoding and decoding, squelch, and gating of audio and data signals. The audio/logic board also has analog circuitry which provides filtering, amplifica- tion, and other processing of the audio, data, and Call Guard signals.

The U101 operating program is stored in Flash EPROM U108. This type of memory can be reprogrammed in the field using the standard programming setup and special programming software. This allows the operating software to be easily updated without the need to change a microprocessor or EPROM. Flash EPROM memory devices retain data indefinitely without the need for battery backup, and can be reprogrammed many times.

Parameters which change from transceiver to transceiver such as programmed system and groups and option key programming are also stored in the

 

February 2001

3-1

Part No. 001-9800-001