Rev. 1.0
Principles of Operation
4—7
The frequency synthesizer also produces a lock signal. This signal is inverted and
buffered to produce both lock and unlock status signals for use in other parts of the
transmitter.
An FSK signal (used for automatic identification of FM repeaters) shifts the
frequencies of the 10.24–MHz crystal reference and the VCO. With keying, diodes in
the in the oscillator are reverse biased, increasing the crystal reference frequency. At
the same time, current through R358 increases the VCO frequency.
The digital management system is located on three boards:
• The metering board
• The metering daughter board
• Front panel controls and display
4.5.1
Metering Boards
The metering boards provide four functions:
• Scale operating parameters from various points in the transmitter to a propor-
tional DC voltage.
• Generate the ALC signal.
• Provide backup to the microprocessor controlled functions on the front panel.
• Provide real-time clock data for the fault log.
4.5.2
Front Panel
The digital management system front panel displays and controls all functions in
the transmitter. Scaled analog signals from the metering are converted to digital
format for display as selected by the operator. Selected values which were created
during a fault are stored for later recall in the fault-log. Real-time audio processing
and modulation is displayed on bar-graph displays; other parameters are displayed
on a four line alpha-numeric display.
Illustration 4-5 Metering Board
Metering
Board
