Comtech EF Data CSAT-6070 - Manual (Page 99)

50 Watt C-Band Transceiver Revision 0
Theory of Operation MN/CSAT6070505.IOM
D.1.2 U
PCONVERTER
The RF input to the upconverter is at 70 ± 18 MHz at a typical level of -35 dBm which
would provide an output power back-off of 8 dB. In operation, the input signal is mixed
up to the 1250 MHz IF in the first conversion mixer operating at a fixed frequency with
low side LO injection at 1180 MHz provided by the upconverter IFLO. IF filtering is
provided by the 1250 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 any
unwanted mixer products, the IFLO, and other spurious signals.
The second mixer up converts the 1250 MHz IF signal to the desired output frequency. It
uses low side LO injection in the 4595 to 5175 MHz frequency range provided by the
upconverter RFLO in 1.000 or 2.500 MHz steps. Both step sizes are automatically
selectable. The upconverted signal is then filtered to reject the RFLO leakage, and any
other unwanted mixer spurs at the mixer output. The output signal is then amplified by a
series of internally matched power FET's to raise the power level of the output signal to
the specified level. An isolator is provided at the output of the high power output stage to
protect it from mismatches at the output connection to the antenna feed.
RFLO IFLO 10 M Hz
REFERENCE
1250 M Hz BPF
1180 M Hz 5175 -
5475 M Hz
6425 - 6725 M Hz
1180 M Hz
70 +/ - 18 M Hz
M & C POWER
SUPPLY
VAR
ATTEN VAR
ATTEN
SSPA
25 WATTS
COM
Figure D-2. Functional Block Diagram of the
Upconverter Section
D-3