Operating instructions

BK RADIO Page 4-1
SECTION IV
THEORY OF OPERATION
4.1 INTRODUCTION
This section contains a description of equipment and a theory of operation for the BK Radio DMH
APCO Project 25 digital VHF radio. To aid in understanding the operation of the equipment,
schematic diagrams are found in Section VI of this manual.
4.2 EQUIPMENT DESCRIPTION
The BK Radio DMH Series radio comprises the following sub-assemblies:
4.2.1 SYSTEM BOARD
This sub-assembly consists of core microprocessor, synthesizer, voltage regulation and baseband
signal processor. A casting is used to shield the synthesizer area.
4.2.2 RX BOARD
This sub-assembly consists of the receiver circuitry from the front-end through the digital IF.
4.2.3 HIGH LEVEL POWER AMPLIFIER BOARD
This sub-assembly consists of the transmitter power amplifier, harmonic filter, antenna switch,
directional coupler and power control.
4.2.4 OPTIONS BOARD
This sub-assembly consists of the audio power amp, and interfaces with both the System Board
and the Control Board.
4.2.5 CONTROL BOARD
This sub-assembly consists of a control head microprocessor, regulator, and vacuum fluorescent
display driver. It interfaces with the front panel.
4.2.6 VCO BOARD
The VCO board is a separate assembly that resides in its own shielded enclosure and
interconnects with the System Board and RX Board.