The E4406a is identified as a "Transmitter Tester" for good reasons. The Transmitters it is testing all have well defined carrier frequencies and were band-limited to less than 10 MHz. It is not billed as a general purpose (Vector) Spectrum Analyzer. Some of the E4406a limitations are:
1) Its maximum "Span" is 10 MHz. This limits it utility as a general purpose Spectrum Analyzer.
2) There is no "Trace Memory" to allow A vs B measurement comparisons.
These limitations and more are addressed by the vsa_gui_1.m application.
Dick Benson (2019). Spectrum Analysis with the Agilent E4406A (https://www.mathworks.com/matlabcentral/fileexchange/69467-spectrum-analysis-with-the-agilent-e4406a), MATLAB Central File Exchange. Retrieved .