[Flexradio] Receiver Sensitivity

[K8MLM]

Is there a simple way to confirm receiver sensitivity?   My receiver front end seems to have lost sensitivity;   I don't hear any change when switching Preamp from "Off" to "Low."  There is a slight change from "off" to "Med."  There is an very slight increase from "Med" to "High."  However, "High" is down significantly from comparison with my FT-1000D (about 3-4 S units).  The difference many times between hearing and not hearing.   It's been my habit to disconnect the antenna when not using the radio.  To trouble shoot, I've changed the entire antenna input (changes coax and switches / exchanged connections with the FT-1000D) line-up to the SDR with no change.  My guess is the receiver front end (Preamp) is out.    Using PowerSDR V1.4.5, Computer - Gateway 3.2 GHz with Delta-44   Thanks,   Bob K8MLM