Operating instructions

Theory of Operation DMH Series VHF Radio

Page 4-2 BK RADIO

4.3 THEORY OF OPERATION

4.3.1 SYSTEM BOARD

System board functions include:

• Core Microprocessor

• Synthesizer

• Voltage Regulators

• Baseband Signal Processor

A. Core Microprocessor

The core microprocessor communicates with the control head microprocessor and the

baseband signal processor. It controls radio functions such as adjusting the deviation and

receiver tuning. An EEPROM is used to store calibration and tuning data unique to each

radio. An internal clock determines the microprocessor’s operating frequency.

B. Synthesizer

The Synthesizer generates an RF signal either to down-convert a desired receive frequency

to a fixed IF or to drive the Transmitter. The synthesizer locks the RF output frequency of a

Voltage Controlled Oscillator (VCO) to a very stable frequency reference.

(1) Synthesizer IC – Contains programmable counters to divide and compare the VCO

output frequency to the stable TCXO reference and adjusts VCO control voltage to

maintain a stable output frequency.

(2) TCXO Reference – Provides a stable frequency reference over the operating

temperature range of the radio.

Steering Line

VCO

Buffer

Loop

Filter

Synthesizer

Buffer

TCXO

Reference

RX/TX

Switch

TX Modulation

Program Line

VCO

Coarse Tune

Filter

Coarse Tune