Hi Warren,
In the technical literature about receivers, they don't use such parameter as "sensitivity". 2 most important receiver parameters that determine whether you can hear the signal or not are: 1. Gain 2. Internal noise.
There is no point in increasing the gain if the signal is drowned in noise.
Your measured the gain of the system that includes Softrock, soundcard and software. You did not measure the internal noise.
I guess both gain and noise stay more or less flat in the case of Softrock, although both get worse towards 30MHz. So your statement about sensitivity being flat is actually true.
However, the number of stations you can hear also depends on the signal and noise levels coming from the antenna. This is why Softtrock "sensitivity" is more than adequate below 14MHz, but is not good enough above 21MHz. On lower frequencies, external noise dominates and drowns weak signals. On higher bands, it is the internal noise that drowns them. Increasing gain doesn't help in this case. Only a preamp with lower internal noise can help. Or a high gain directional antenna, if you don't need omnidirectional receiving.
73, Mike
