[Elecraft] waterfall/fft sensitivity ...

[John Ragle]

  Larry...

     Your rejoinder to "Bill" doesn't specify mode, so I am assuming CW. 
I don't use either P3 or L-PAN yet, but I do use the similar 
visual-signal part of fldigi. A PSK or RTTY signal has an "idle" signal 
which will average to a visible signal if you are using some degree of 
fft accumulation. I usually use a 4x accumulation with fldigi, and weak 
signals are often discernible at this degree of averaging (for 
PSK/RTTY), but of course CW has no idle signal, and has a fairly low 
duty cycle as well. In my experience, with NO fft accumulation very weak 
CW signals do not show in the noise., even though they are copyable by ear.

     All this says nothing about the ability of software to decode 
signals, and (again for example) fldigi will show the railroad tracks of 
a PSK signal without being able to produce copy. The eye is designed by 
nature to discern linear features (even when they are not there).

     The ear is a remarkable instrument for picking up signals! With fft 
processing there is always the question of passband, but the ear has its 
own built-in "Q-fivers," which kick in for CW.

     I am not at all surprised that you can hear signals that the P3 
(and its cousins) do not show.

John Ragle -- W1ZI