Specifications

CHANNEL SELECTOR

One of 16 channels may be selected using the Dip Switch (SW401) and serial commands. The

hardware selector, SW401 encodes the channel number, selected into 4-bit binary code. The

binary code plus one equals the channel number. The binary code is decoded by the CPU,

which enables the appropriate RX or TX frequency and associated data to be selected from the

EEPROM. External serial commands which come from Pin 8 of the DB-15 Connector (CON401)

are fed into Pin 41 of IC401 (MCU). The micro controller uses UART (Universal asynchronous

receiver transceiver) for serial communication and decodes serial commands in order to control

the radio.

DC TO DC CONVERTER

The main DC power is supplied to the switched mode DC to DC converter . The DC to DC

converter regulates the various input power supply voltage and outputs a constant voltage of

6.5 Volts (SD-161, SD-164) or 7.5 Volts (SD-171, SD-174). It is a source for all of the RF and

digital circuits. The DC to DC converter is formed by IC801, Q801, Q802, L801, R804 and

voltage divider(R805, R806, R802). IC801 is a PWM controller that controls pulse width of the

switching pulse output. Various input voltage appears as various output voltage of voltage

divider. IC801 detects the voltage difference between inner reference voltage and the voltage

divider output controls the switching pulse width in proportion to its difference. Wanted output

voltage is decided by product of input voltage and duty ratio of switching pulse. As the switching

pulses, Q801and Q802 switch the input DC of various supply voltages and generate the

constant DC of supply voltage. IC801 controls maximum current of DC to DC converter by

current detection through voltage drop of R804.