Comtech EF Data CSAT-5060 - Manual (Page 22)

C-Band Transceiver Revision 1
Introduction MN/CSAT5060.IOM
1-4
1.3 RF S IGNAL C ONVERSION
1.3.1 D
OWNCONVERTER
The RF input to the Downconverter is in the 3400 to 4200 MHz frequency range at a typical level
of -45 dBm. The input signal is mixed down to the 1110 MHz IF in the first conversion mixer.
High side LO injection is used for this mixing process. The Downconverter RFLO synthesizer in
the 4510 to 5310 MHz frequency range provides it in 1.000 or 2.500 MHz steps. Both step sizes
are automatically selectable.
IF filtering is provided by the 1110 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 1110
MHz. It operates with high side LO injection at 1180 MHz provided by the Downconverter IFLO
and converts the IF signal down to the 70
±18 MHz output frequency.
RFLO IFLO
1 0 M Hz
REFERENCE
1 1 1 0 M Hz BP F
1 1 8 0 M Hz 4 5 1 0 -
3 4 0 0 -
5 3 1 0 M Hz
3 4 0 0 - 4 2 0 0 M Hz
1 1 8 0 M Hz
7 0 +/ - 1 8 M Hz
M & C P O WER
SUP P LY
V A R
A TTEN V A R
A TTEN
4 2 0 0 M Hz
CO M
Figure 1-1. Functional Block Diagram of the Downconverter Section