HP 8517B manual LO Signal Control

	Troubleshooting the Test Set
	Theory of Operation
	• If the test set is equipped with Option 001 (multiple test set capability),
	its begin state is inactive. That is, rather than using the test set’s internal
	IF, a switch is set in the test set to accept an IF from another test set.
The LO Signal Control	The LO, generated by A14 VTO/driver, is phase locked to the source so the
	desired VTO harmonic is 20 MHz greater than the source frequency.
	The phase-locked loop includes:
	• Portions of the test set, such as the VTO summing-amp board (A3), the
	VTO/driver (A14), and the a1 sampler assembly (A10), and
	• The HP 8510C Network Analyzer
	The VTO summing-amp board (A3) provides control voltages to tune the
	VTO to the correct LO frequency.
	The VTO also has an output LENDRA (Low END of RAnge) which is
	routed via the test set interconnect cable, to the HP 85102.
	The LENDRA provides an indication to the network analyzer about whether
	or not the VTO is operating within its normal frequency range.
	If the VTO exceeds its normal frequency range, the network analyzer
	displays the running error message VTO OVER RANGE.
CAUTION	Electrostatic Discharge Sensitive (ESD) Assemblies
	Assemblies you might handle in these troubleshooting procedures are
	extremely sensitive to damage from static electricity. They may or may not
	continue to function if they are subjected to electrostatic discharge. Their
	reliability, however, will be impaired.

5-4HP 8517B S-Parameter Test Set Manual