Instruction Manual

DE
DANIELS
ELECTRONICS
2-6 Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz
2.3 Synthesizer Digital Circuitry (Digital Board)
Refer to the "OS(R/T)-3(A/H) Digital Board Schematic Diagram" on page 4-19. Microcontroller
U4 provides control of the synthesizer module. It communicates with synthesizer IC U10,
monitors the synthesizer lock detect, manages PTT input/output, and determines the operating
frequency from either four rotary BCD switches or four externally driven channel select lines. The
rotary BCD channel switches are located on the main MT-3 Transmitter or Receiver circuit board.
The Microcontroller U4 also communicates with an external factory programmer through I/O lines
TX DATA (P1-17), RX DATA (P1-9), and BOOTSTRAP (P2-2). The external programmer
places the operating program in non volatile microprocessor memory. It is also used to program 15
user defined channel selections. An internal "watchdog" timer provides robust software protection
in all operating modes.
Data communication between the digital and analog circuit boards is provided by four optical
transmitters (U5 through U8) and one optical receiver (U9). The optical interface provides a fully
isolated inter-board data link designed to eliminate digital noise from disturbing sensitive PLL
circuitry.
2.4 Frequency Control
2.4.1 BCD Switch Frequency Control
Selection of the desired synthesizer output frequency is straight forward. If all four of the channel
select lines CHAN SEL3 - CHAN SEL0 are pulled low (grounded), the synthesizer will scan four
BCD switches connected to SW1 COM - SW4 COM and PC4 - PC7 to establish the operating
frequency. The BCD switches are located on the receiver and transmitter main circuit boards.
* Note: The four channel select lines, CHAN SEL3 - Chan SEL0, are connected via the MT-3
transmitter or receiver main board module connector to the M3 motherboard subrack. These lines
may be used for external frequency control. They are normally pulled low via jumper sets located
on the M3 motherboard subrack.
If the channel select lines are pulled high to +9.5 Vdc in any combination resulting in a binary code
greater than 0000 (all low), then the frequency is established as the preprogrammed entry in a table
containing 15 separate frequency settings. For example; if all the channel select lines are pulled
high then a binary code of 1111 results which selects the frequency entry from the 15th table
position. CHAN SEL3 is the most significant bit of the binary channel selection code. The channel
table is normally programmed at the factory for those applications requiring specialized remote
control of frequency. These programmed channel assignments are stored in non-volatile
microprocessor EEPROM and are not susceptible to inadvertent erasure.
In transmitters, the synthesizer operating frequency is the transmitter operating frequency;
however, for receivers, an IF Offset correction factor (21.4 MHz typically) must be added to or