Specifications

Table Of Contents
MAINTENANCE
Page 116 MRC-565 Packet Data Radio Operations & Maintenance
6.1.3 Digital Transmitter Components
The transmit modulation path (TX exciter) starts with the CF, proceeds to the DSP, the FPGA
and finally the Quadrature Digital Up Converter (QDUC). The QDUC outputs low level RF
directly on the assigned carrier frequency. That signal is passed to the RF power amplifier PCA.
Refer to the transmitter signal processing block diagram Figure 16 for the ensuing discussion.
Master
Microprocessor
MCF54455
(U50)
Digital Signal
Processor
TMS320C5510A
(U8)
FPGA
EP3C10
(U37)
Interpolator
25
Interpolator
200
Modulator
480MSPS
DAC
480MSPS
SIN/COS
Lookup
Tables
Direct Digital
Synthesizer
(NCO)
Clock PLL
480MHz
(19.2 x 25)
TXCO
19.2 MHz
DAC
AD5318
(U23)
TXCO
25 MHz
Phase
Quadrature
Digital Up-
Converter
AD9957(U63)
RF
Data
src
NRZ
Data
I
Q
96
ksps
I=in-phase, Q=Quadrature-phase
baseband data modulation
CAL
Voltage
Power and
Control Paths
Not Shown
50MHz
Low Pass
Filter
50MHz
Low Pass
Filter
TX/RX
Switch
TX LOW
PASS
FILTER
Coupler
RF
Detector
DC Amp
(U2)
A2
40-46 MHz
10,25,50 or 100 watts
Two Stage Class C RF
Power Amplifier
RF Preamp
RFPA PCB
CMU PCB
RF
U1 - HMC589A Q1 - L2711
XFMR
2:1
R100HHHFIC
Q2 & Q3 R100HHHFIC
XFMR
1:5
Transmit Digital Section
Transmit Analog Section
A1
Q2
Q3
A3
Figure 13. Transmitter Block Diagram
6.1.3.1 TX LO and Exciter
The transmitter carrier is generated and then modulated by the Quadrature Digital Up-Converter
(QDUC) IC (U63). A control path (not shown) from the master processor operating system (OS)
passes carrier frequency selection commands to the QDUC direct digital synthesizer (DDS).
The QDUC is multifunctional. First, it uses a phase locked loop (PLL) to multiply the TCXO
frequency to (19.2 * 25) = 480 MHz. This serves as the precision sample clock for a direct
digital synthesizer (DDS) inside the QDUC. The carrier frequency is generated by the
accumulator in the DDS numerically controlled oscillator (NCO). The available resolution is 100
Hz and the output frequency range is 40 to 47 MHz Because of the PLL tracking loop, the
frequency accuracy and stability of the carrier is proportionally the same as the TCXO. The