Comtech EF Data CST-5000 - Manual (Page 103)

Theory of Operation CST-5000 C-Band Satellite Terminal
5–14 Rev. 9
5.4 Synthesizer
The RFT-500 uses two synthesizers (optional single synthesizer):
• One for the down converter to convert the RF input to a 70 MHz IF output
• One for the up converter to convert the 70 MHz input to the RF output
The purpose of the synthesizer module is to convert the 10 MHz reference signal to a
variable frequency to perform the conversion. A single synthesizer option is available.
When the up converter is programmed, the down converter frequency is automatically
selected.
5.4.1 Specifications
RF Inputs:
Connector type
Impedance
Input level
10 MHz CMOS square wave
2120 MHz reference (from IFLO)
SMA
50
Ω
+7 dBm
RF Outputs:
Connector type
Impedance
Level
U/C frequencies 4715 to 5295 MHz
D/C frequencies 4610 to 5190 MHz
Single 4662.5 to 5242.5 MHz
SMA
50
Ω
+7 dBm
5.4.2 Theory of Operation
The synthesizer module multiplies the 10 MHz reference clock to a variable clock by use
of:
• VCOs
• Loop filters
• Phase detectors
• Variable divide-down chain
The divide-down chain is controlled by the M&C board through the use of 14 parallel
CMOS signals. The down converter divide-down chain varies from 150 to 380. The up
converter divide-down chain varies from 222 to 422. A frequency doubler is then applied
to produce the final output.
The VCO tuning voltage is sent to the M&C for monitoring, as well as a lock detect fault.
Refer to Figures 5-6 and 5-7 for block diagrams of the down and up converter LO
synthesizers.