Specifications

4-6 888-2857-004 5/9/13
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
Platinum VAX-C Series
4.4.1 Signal Processor Board Overview
The signal processor board serves as a motherboard for the UAC-C Transmitter
modulator. The board interfaces to all the boards in the modulator. Refer to Figure 4-2
on page 4-5.
The signal processor board also serves as the ASI input and output, decoder and
encoder, the modulator, the digital precorrector (RTAC circuit for digital modulation
modes), and it contains the ADC and DAC which interfaces to the up/downconverter
board RF connections. The signal processor board has control interfaces to the
transmitter I/O Interface board, the PA Interface board (which in turn connects to the
up\down converter board), the PFRU board, the front panel, and the LVPS.
Power for the signal processor board is derived from the LVPS, which delivers +5Vdc,
+12Vdc, -12V, +24Vdc, and +12VBATT. All other voltages necessary for the signal
processor board are derived from these inputs. All boards receive their power through
the signal processor board.
Monitoring of the power supplies and ambient temperature are performed by the micro
module, which is a daughter board mounted on the bottom right, rear corner of the
signal processor board. The micro module also initiates offline tests requested by the
user, such as memory tests, serial channel loop back, predefined board level tests, and
predefined LPU tests.
4.4.1.0.1 DAC
The DUC writes the 16-bit I and Q data to the AD9779 DAC. The DAC will be clocked
by the ~409 to 460 MHz clock from the PFRU. The 1/4 F
DAC
clock output of the DAC
is used as a clock for the DUC FPGA and the RF Sample ADC. The DAC will provide
the Up/Downconverter board with the 140MHz IF at a 0 dBm average level.
4.4.1.0.2 ADC
The AD9461 ADC will be clocked by the 1/4 FDAC clock. It will convert the 140 MHz
IF from the downconverter to a 16 bit sample provided to the DUC FPGA. The ADC
will also provide the DUC FPGA with the Sample A/D clock.