Can I convert my 1.5 GHz ESA Spectrum Analyzer input impedance from 50-ohm to 75-ohm or vice versa from 75-ohms to 50-ohms?

Keysight does not supply a specific upgrade kit to change the input impedance of the Spectrum Analyzer. It is not a simple connector change, rather an entire R.F. assembly, model ID label, and connector label. Here is a listing of parts that would have to be changed out in order to convert your Spectrum Analyzer. Description 50Ω Part Number 75Ω Part Number   E4401-60294 E4401-60100     E4411-80013 Model ID Label (E4401B) E4401-80027 E4401-80028 Connector Label E4401-80003 E4401-80002 Note: The analyzer CANNOT have a 50Ω Tracking Generator, option 1DN and be used with a 75Ω input impedance, option 1DP. Similarly, the analyzer CANNOT have a 75Ω Tracking Generator, option 1DQ and be used with a 50Ω input impedance. The Tracking Generator output impedance MUST match the analyzer input impedance or the analyzer will not be able to be calibrated at an Keysight Service Center. Once the R.F. assembly is changed the following tests must be performed in order for the analyzer to meet published specifications. Adjustments: Frequency Response An ESA Signal Analyzer can only be adjusted using the N7800A field test software.  This software also requires specific test equipment, so in most all cases adjustments must be performed at a Keysight Service Center. Performance Tests: 10 MHz Reference Accuracy Noise Sidebands Sytem-Related Sidebands Residual FM Frequency Span Readout Accuracy Fequency Readout and Marker Count Accuracy Absolute Amplitude Accuracy Frequency Response Spurious Responses Gain Compression Other Input Related Spurious Responses Displayed Average Noise Level Residual Responses A complete listing of analyzer performance tests and the test equipment requirements can be found in the ESA Spectrum Analyzer Calibration Guide.