General Dynamics CG-1220, Operation And Maintenance Manual

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Theory
2.0 THEORY
2.1 Standard L-band DTR
The use of advanced DSP techniques coupled with conventional analog radio
techniques provides enhanced flexibility and sensitivity to the DTR.
The L-Band DTR, illustrated by the block diagram in Figure 2-1, takes a RF input
signal in the L-Band frequency range and down-converts the signal to a 70 MHz
Intermediate Frequency (IF) using a super-heterodyne process. The signal is then
routed through an anti-aliasing filter prior to being sampled by a high-speed analog
to digital converter (A/D). This digital data is then passed through a decimating
Finite Impulse Response (FIR) filter, which provides both a sample rate reduction
and a band limiting function.
The DSP chip then transforms the data using a Fast Fourier Transform (FFT) and
analyzes the band for signal and noise content. The signal power and signal to
noise information is estimated and the values are sent to the System Control
Processor (SCP).
The SCP sets and manages module functions and communication with the user
and other equipment via the front panel controls and data interfaces. The SCP also
makes slope adjustments and reports the received signal power level to control
equipment via serial communications.
Analog to
Digital
Conversion-
RF Front-End
DSP
MCU
DDS
Frequency
Reference
Control
Graphics Display
(240x64-pixel)
Keypad
+
SoftKeys
RS-232 Serial
Ports
RS-422 Serial
Ports
SRAM
Flash
EEPROM
SCP
Analog/Customer
Interface I/O
I/O
16-Bit Parallel (DMA)
166X32K
Synchronous
FIFO
FIR
Filtering
Serial Link
Serial Link
PLL Reference(s)
Control
IF
Monitor
Port
SPU
CPU
Signal of Interest
Digitized
Signal
Filtered Signal
Flash
EEPROM
NVRAM
RS-485 Serial
Port
Figure 2-1 DTR Block Diagram
CG-1220 DTR 2-1