User Manual Part 1

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SECTION 5 CIRCUIT DESCRIPTION
5.1 GENERAL TRANSCEIVER DESCRIPTION
5.1.1 INTRODUCTION
The E.F. Johnson 4300 is a microcontroller-based radio that uses a Digital Signal Processor
(DSP) to provide the following modes of operation:
Narrowband Analog - FM modulation with a maximum deviation of 2.5 kHz. This mode is
usually used in systems where the channel spacing is 12.5 kHz. Call Guard (CTCSS or DCS)
subaudible squelch signaling can be used in this mode.
Wideband Analog - FM modulation with a maximum deviation of 5 kHz. This mode is usually
used in systems where the channel spacing is 25 kHz or 30 kHz. Call Guard (CTCSS or DCS)
subaudible squelch signaling can be used in this mode.
Project 25 Digital - The voice is digitized, error corrected, optionally encrypted and transmitted
using C4FM modulation according to the Project 25 standard. This mode can be used in channel
spacings of 12.5 kHz.
DES Encryption -This mode is compatible with the Motorola DES protocol. Voice is digitized,
encrypted, and transmitted using FSK modulation. This mode can be used in channel spacings of
25 kHz. The DSP processes the received signals and generates the appropriate output signals. The
microcontroller controls the hardware and provides an interface between hardware and DSP.
5.1.2 PC BOARDS
The 4300-series mobile contains the following PC board assemblies:
RF Board -Contains the receiver, synthesizer, and exciter sections.
PA Board -Contains the transmitter power amplifier, power control, and main DC power
switching sections.
Logic Board - Contains the digital signal processing (DSP), control logic, and audio processing
sections.
Interface Board - A small board that provides the electrical connections between the logic and
RF/PA boards. It also contains the audio amplifier and volume control circuits for internal and
external speakers.
Display Controller - Contains a microcontroller which provides an interface between the
controller on the logic board and the front panel display and switches.
Display Board - Contains the liquid crystal display, option switch keypad, and display drivers. In
addition, it contains the backlight for the display and keypad.