Hi Andy
>Is the S/N calculation being a bit optimistic? The
calculation in WSJT / WSPR gives an artificially high S/N value if the input
bandwidth is restricted below >a complete 2.5kHz's worth, and if impulsive
noise is present. So could ROS be suffering some similar effect?
I think the reports should be taken as ‘As
Indicated By’ - WSPR or ROS. I have no idea how the S/N figure is
produced but by observation in both systems it is obvious that averaging goes
on.
Last night some of my S/N figures from ROS
of -31dB were from a frame which had QSB -25dB short peaks and -35db troughs.
I have a WSPR capture from 6m in which my
signal is decoded 51Hz lower than the signal frequency, due to Aircraft
Doppler. The reflection is logically and visibly much weaker than the direct
path signal. Yet WSPR has reported it only 1dB lower. The report is enhanced by
another reflection from another Aircraft which is much stronger and does not de-code
due to a 15Hz plus varying Doppler shift, it sweeps down in frequency and joins
the decoded reflection for less than on third of the data period.
These are real life happenings, quite
different from laboratory figures.
If the AS description sounds like Chinese,
I can see the critics saying 51Hzis due to mains hum already, it isn’t. I
can point you to the screen grabs and tests we were doing.
