User Manual

Technical Description
Version 4 4-1 04/02/04
4 Technical Description
4.0 Overall System
The Extend-A-Page VHF transmitter consists of:
1. Control “U” Board
2. Control “A” Board
3. Synthesized Exciter
4. Front Panel Display Board
5. Power Supply
The overall control system is shown in the Overall Block Diagram Page A-
20. The Control “U” board in Fig. 3-D handles the frequency setup of the
RF exciter and the modulation on the 10.7 MHz I/F. The Control “U” board
also supervises the internal switching on the Control “A” board that allows
the deviation limits to be set separately on the two different data paths, the
analog modulation, and the digital modulation respectively. The composite
analog signal is sent to the Control “U” board and filtered and sampled at
20 KHz. The digitized signal is then used to digitally deviate the NCO to
generate the instantaneous signal for the 10.7 MHz I/F. The maximum
deviation is limited to +/- 5 KHz.
4.1 CONTROL U BOARD
The purpose of the Control U PCB is to interface the data and key control lines
for the data to be transmitted and setup the center frequency and the control
modes to the transmitter modules. The data, key line, and frequency select data
comes into the unit from the network diagnostics connector on the backplane.
The Control U PCB senses the key line and samples this data with the
AT89LS8252 microprocessor. The microprocessor has a power up delay to allow
the hardware reference oscillators to stabilize. It then sends the setup data to the
RF exciter to set its center frequency with serial programming data and clock to
the power exciter. The microprocessor then enters a continuous loop waiting for
the key signal. The key signal is debounced. After the microprocessor detects the
debounced key signal, it samples the frequency select lines to determine the
center frequency. The microprocessor then sends the setup data that
corresponds with that frequency to the RF exciter. The data and clock lines are
continuously sampled and mapped in the Altera chip (U1) depending on the SW1
switch modes on the Control U and then sent to the RF exciter.
In the analog mode the Control “U” board sends the SC3, SC2, SC1, SC0 signals
switch lines to the Control “A” board to control the data path that is to be
transmitted. The composite analog signal is sent to the Control “U” board and
filtered and sampled at 20 KHz. The digitized signal is then used to digitally