Comtech EF Data CST-5000 - Manual (Page 126)

CST-5000 C-Band Satellite Terminal 140 MHz IF Option
Rev. 9 A–7
A.1.3.2 Theory of Operation
The RFT-500 down converter utilizes a dual conversion process to convert from an input
frequency band of 3620 to 4200 MHz, to an output baseband 140 MHz IF signal.
The first conversion requires a synthesizer frequency input to mix with the RF input. The
M&C board controls the frequency selection of the synthesizer. The synthesizer output
frequency band is 4592.5 to 5172.5 MHz, in 2.5 MHz steps.
The output of the first mixing process is at a frequency of 972.5 MHz. The 972.5 MHz is
applied to the second mixer, which mixes with an IFLO frequency input at 1112.5 MHz
from the IFLO module.
The output of the second mixer is the desired baseband 140 MHz IF signal.
The M&C board interpolates the factory present compensation data that is stored in an
EEPROM inside the down converter. This data allows the M&C board to command and
compensate the down converter’s output power, ensuring proper output levels over the
entire frequency and temperature range. The M&C board also supplies the DC power for
the LNA, which is subsequently injected into the RF input connector.