Comtech EF Data CSAT-6070 - Manual (Page 110)

5 to 25 Watt C-Band Transceiver Revision 0
Theory of Operation MN/CSAT607025.IOM
D.1 RF S
IGNAL
C
ONVERSION
D.1.1 D
OWNCONVERTER
The RF input to the downconverter is in the 4500 to 4800 MHz frequency range at a typical level
of -45 dBm. The input signal is mixed down to the 1590 MHz IF in the first conversion mixer.
High side LO injection is used for this mixing process. It is provided by the downconverter
RFLO synthesizer in the 5830 to 6130 MHz frequency range in 1.000 or 2.500 MHz steps. Both
step sizes are automatically selectable.
IF filtering is provided by the 1330 MHz BPF. It is just wide enough to pass the 36 MHz
bandwidth of the desired signal while maintaining more than adequate amplitude and group
delay flatness. At the same time, it is narrow enough to provide the necessary rejection to the
image, the RFLO, and other spurious signals. The second mixer operates at a fixed input
frequency of 1330 MHz. It operates with high side LO injection at 1400 MHz provided by the
downconverter IFLO and converts the IF signal down to the 70 ±18 MHz output frequency.
Figure D-1 Functional block diagram of the downconverter section
D–2