Hi Euan,
Good questions,
The marker “Set Freq” entry was designed as a one way control. It doesn’t show you the current marker frequency, but can be used to set the marker frequency. This is why you don’t see it ever update until you manually type something into the box. So things like moving the marker, or loading presets will not affect it.
As for why you don’t see the marker frequency report exactly what you set, is because the sweep bins do not always land on nice round frequencies. So when you set 1.83GHz, it will find the closest frequency point to your value. What frequencies bins the sweep lands on are hardware and configuration specific and are not predictable. RBW controls how close sweep bins are, so as long as your RBW is good for your application, using the set freq will always choose a sweep bin within your RBW, which would presumably be sufficient.
Let me know if you have follow up questions.
