The Lo Signal Control - HP 8517B Operating & Service Manual

The LO Signal Control

CAUTION
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, 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
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.
5-4 HP 8517B S-Parameter Test Set Manual
VTO OVER RANGE.