Sample Rate - Calibration Bandwidth - Low Pass Filter Bandwidth - Noise floor


I have some nagging “newbie” questions that I can’t find definitive info on.

I’m using my LimeSDR as an RX on HDSDR using the ExtIO. I am trying to work out the relationship between sample rate bandwidth, the calibration bandwidth and the LPF bandwdith. The calibration bandwidth range (and LPR) is from 2.5 to 120Mhz, yet the sample bandwidth is limited to 30Mhz. Are the 3 related to each other ?

If I select 4mhz sample bandwidth the calibration and LPR bandwidth also goes to 4mhz automatically. LPR completely wipes everything out at 4Mhz, (I don’t understand the LPR bandwidth) so I need to turn LPR off.

It is then very hard to calibrate at 4Mhz with the LPR off, it takes 5-10 tries to get it to calibrate.

Can I use a different calibration value than the sample bandwidth value ? 50Mhz calibration and LPR On seems to work well. Can I use 50Mhz calibration bandwidth with 4Mhz sample bandwidth ? T

Also is it true that the noise floor will be lower using 4Mhz sample rate than say a 30Mhz sample rate ? So lower sample rates will increase sensitivity ?