Chapter 2 79
Block Diagrams
A18 Reference Assembly
300 MHz Output
The 300 MHz output provides the 2nd LO signal and the LO signal for
the IF calibrator on the A17 RF assembly.
Reference Unlock Detector
If the A18 reference assembly is not receiving the correct reference
signal, an unlock error message will appear in red text in the
annunciator bar on the front panel. This state is detected by the A22
CPU assembly from the A18 reference assembly.
50 MHz Calibrator Output
The 50 MHz (100 MHz x 2) internal calibrator is used to perform
background calibration on various assemblies in the instrument. This
signal is routed to the A17 RF assembly where it is level shifted.Š
10 MHz Outputs
The 100 MHz VCXO, which is phase locked to a frequency reference, is
divided by ten, resulting in a 10 MHz signal. This signal is used on
various assemblies in the instrument, including the A22 CPU, A17 RF,
A12 analog IF, A18 reference, the output to the rear panel (switched),
and the A19 synthesizer.
Interconnections to other assemblies
• A18J2P13. External reference in (1 to 30 MHz) from the A15
daughterboard.
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