Hi Volgy,
Nice work for being new at this! You have largely properly characterized the functionality of the fast sweep mode. There is only one more thing to know about. To accomplish “arbitrary” RBWs, you can perform FFT zero-padding. This basically gets us the ability to configure for RBWs as if we have FFT sizes between 16 (or whatever we use as the smallest) and 16384, in increments of 1, and not just 512,1024,…,16384.
And to address your other question, you are correct, the detector is not relevant for the reason you listed.
If you need more flexibility than what fast sweep mode offers, take a look at the I/Q sweep list. This mode lets you preconfigure a list of freq steps and I/Q capture sizes, and executes them at the same speed as fast sweep mode. This gets you the time domain I/Q samples as opposed to the processed spectrum data. On the SM435C, the I/Q bandwidth for each “step” is 160MHz, so you can achieve > 1THz sweeps with the right settings. For the SM435B models, the I/Q bandwidth is only 40MHz, so it falls short of 1THz per second, and in that case the fast sweep mode is providing functionality that I/Q sweep lists cannot. The downside of I/Q sweep lists is that now you have to do your own processing, but it will let you reproduce most of the sweep capabilities offered through the sweep modes.
