Why does the N5530S Measuring Receiver require Option 123 (Preselector Bypass) above 3 GHz?

The N5530S Measuring Receiver System is comprised of a PSA Series Spectrum Analyzer, an EPM Series Power Meter, an N5532A Sensor Module, and N5530S Measuring Receiver Software.

The PSA YIG Tuned Filter (YTF) is tuned by a magnetic field. The magnetic field is generated by sourcing current through electromagnets. The tuning current self-heats the YTF, and this heating induces frequency drift. The frequency drift results in amplitude errors versus time. Option 123 is a down conversion path that bypasses the YTF, thus eliminating the amplitude errors induced by YTF drift above 3Ghz.