Keysight N5227A Service Manual page 131

PNA Series Microwave Network Analyzers Theory of Operation
N5227A Synthesized Source Group Operation
external reference signal is detected at the 10 MHz EXT REF IN port on the rear panel, it is used as the
frequency reference instead.
The 10 MHz reference signal is used to phase lock a 100 MHz VCO. The output of this VCO is then divided by
ten to produce the 10 MHz EXT REF OUT rear panel signal and also a 10 MHz reference signal for the A16
signal processing ADC module (SPAM) board. The VCO output is also divided by two to produce 50 MHz
reference signals for the A4, A15, and A17 13.5 GHz synthesizer boards.
Service Guide N5227-90001 5-15