Comtech EF Data CST-5000 - Manual (Page 107)

Theory of Operation CST-5000 C-Band Satellite Terminal
5–18 Rev. 9
5.5.2 Theory of Operation
The RFT-500 down converter utilizes a dual conversion process to convert from an input
RF frequency band of 3620 to 4200 MHz, to an output baseband 70 MHz IF signal.
The first conversion requires a down converter 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 from 4610 to 5190 MHz, in 2.5 MHz steps (optional
125 kHz step size available).
The output of the first mixing process is at a frequency of 990 MHz. The 990 MHz
output is applied to the second mixer, which mixes with an IFLO frequency input at 1060
MHz from the IFLO module. The output of the second mixer is the desired baseband 70
MHz IF signal.
The M&C board interpolates the factory preset 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 power 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.