Chapter 12 12-21
Theory of Operation
Source Theory Overview
The analyzer normally goes through a pretune-acquire-track sequence to achieve phase
lock. In external source mode, the fractional-N VCO pretunes as a closed-loop synthesizer
referenced to the 100 kHz signal from the A12 reference assembly. Then, to acquire or
track, a switch causes the VCO to be tuned by the A11 phase lock assembly instead. (Refer
to the Overall Block Diagram at the end of Chapter 4 , “Start Troubleshooting Here.”)
Figure 12-7 External Source Mode
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