Hi Jom,
The SA124B and BB60D serve different use cases. The SA124B is a narrow band analyzer (250kHz bandwidth) ideal for making measurements on narrowband signals, such as CW, AM, FM. Using the SA124B to measure wideband modulated signals such as the radar or comms signals that might exist at X-band frequencies would be ill-suited/impossible. The BB60 is much better for measuring wideband signals. If you need BB60 like performance to X-band frequencies then you need to look into the SP145 or SM200, which are much closer to the BB60 in capability.
Both the SA124 and BB60D are capable of making phase noise measurements. The BB60 will make those measurements several times faster. The phase noise measurement performance floor is limited by the analyzer itself. If you have specific measurement requirements for phase noise, I can verify you will be able to accomplish them with either device. The phase noise license is tied to a single S/N device, and we have both annual and perpetual license options.
Let me know if you have follow up questions or comments.
