Chapter 5 119
Troubleshooting the Synthesizer Section
A11 Reference Assembly Description
100 MHz VCXO
The 100 MHz voltage controlled crystal oscillator is used as the main
reference in the instrument. It is phase-locked with either an internal
or external frequency reference. The overall frequency accuracy of the
instrument is determined by the accuracy of the frequency reference.
300 MHz Outputs
There are two 300 MHz outputs. The first 300 MHz output provides the
3rd LO signal and the LO signal for the IF calibrator on the A10 3rd
Converter assembly.
600 MHz Outputs
There are two 600 MHz outputs. One is routed to the A12 Synthesizer
assembly, and the other is routed to the A9 2nd LO assembly.
Reference Unlock Detector
If the A11 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 A26
CPU assembly from the A11 reference assembly.
50 MHz Calibrator Output
The 50 MHz (100 MHz ÷ 2) internal calibrator is used to perform
background calibration on various assemblies in the instrument. This
signal is routed to the A10 3rd Converter assembly where it is level
shifted.
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 A26 CPU, A13
front end driver, A8 analog IF, A12 synthesizer assembly, and the
10 MHz output to the rear panel (switched).
Interconnections to other assemblies
• A11P1. External reference input (1 to 30 MHz) from rear panel.
• A11P2. 10 MHz output to rear panel.
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