HP 8712ET User Manual page 264

Calibrating for Increased Measurement Accuracy
Checking the Calibration
Isolation Isolation is a measure of crosstalk between RF signal
paths. For example, there may be leakage between the
RF OUT and RF IN signal paths inside the analyzer.
The isolation term displays the best possible noise floor
of a transmission measurement with no external signal
path.
This measurement can be in the range of −120 to
−85 dBm.
Typical Isolation Error Term
Figure 6-10
6-38 ET User's Guide