Comtech EF Data SFC4200 - Manual (Page 41)

SFC4200/SFC1275G Synthesized Frequency Downconverter User Interfaces
TM054 - Rev. 4.0 4-17
4.2.10.1 Reference Offset
The Reference Offset Field of the Reference Menu allows the operator to adjust the frequency of
the 10 MHz High Stability Internal Reference and vary the output of the Synthesized RF LO by
±
999 Parts per Billion (PPB). One part per billion represents a change of 1 Hz per GHz (1 billion
Hz) of output frequency. Measured at the LO MON port, 1 PPB represents 4.6 Hz change in
frequency for a LO Output of 4.6625 GHz. Note that 1 PPB changes the frequency of the LO
MON or Converted IF or RF Output by 4.6 Hz as well. Thus, each unit of PPB will allow a
change in accuracy of the converter of 1 x 10
-9
.
The exact frequency of the LO Output can be calculated from the displayed frequency on the
converter front panel as follows:
C-Band Downconverter (70 MHz IF): LO MON = Rx Freq. + 1042.5 MHz
C-Band Downconverter (140 MHz IF): LO MON = Rx Freq. + 972.5 MHz
C-Band Downconverter Extended (70 MHz IF): LO MON = Rx Freq. + 1155 MHz
C-Band Downconverter Extended (140 MHz IF): LO MON = Rx Freq. + 1085 MHz
Ku-Band Downconverter (70 MHz IF): LO MON = Rx Freq. – 2070.0 MHz
Ku-Band Downconverter (140 MHz IF): LO MON = Rx Freq. – 2140.0 MHz
The RF Monitor output can be measured with a frequency counter of known calibration.
4.2.10.2 Reference Stability
The stability of the 10 MHz Reference is related to the temperature of 10 MHz crystal inside the
unit. A proportionally controlled oven around the crystal maintains the temperature in the oven
to 0.1°C. In addition, the precise temperature that the oven maintains has been determined
empirically for each crystal during manufacturing. As long as the ambient temperature stays
within limits (0 - 50
°
C) the reference will maintain stability of greater than 1 x 10 -8 (refer to Figure
4-18).
Figure 4-19. Typical Reference Aging vs. Time