The biggest problem with my SDS200 is that digital transmissions often sound muffled or garbled, even when the signal strength is high. Does the 150 improve on that?
Set the display to show digital bit errors, D-error, and if that show a low value below 5 then it is the portables/mobiles in the system that are received poorly by the system, or if the dispatchers can be heard clearly but mobiles worse.
If you always have full signal from a system then try and enable the attenuator to bring the signal down in level. It can be a too strong signal that makes reception worse in the scanner. The receiver in SDS scanners overloads very easily compared to other scanners.
/Ubbe