NEW: panadapter adjustment against the noise floor

[dl1bz]

I add the option now to adjust the scaling of the pandapter/spectrum display against the noisefloor. The adjustment works only for the lower part of the scale, the higher part is set to -55db, but can be increased by the user. Lower values < -55db will be set back to -55db for the upper value. We measure with the user-defined framerate (e.g. 25fps means 25 times per second) the noisefloor for 1s and and form the average. This is repeating every 1s. We round the value down and add -5db lower, e.g. measure noisefloor -115db, add -5db = -120db. This value will be set as the lower value for the panadapter and will be checked continuously and, if required, re-adjusted.

The Automatic can be switched ON in the Display Menu, if ON, the manual setting of the lower pandapter value is closed and not accessible, the upper value can be changed nevertheless with Automatic ON.
In the VFO surface we have now a new display NFA ("Noisefloor Automatic"), it's green when it's ON, grey when it's OFF.

Notice: The calculation of the current noisefloor is not a simple thing. And this value is of course fluctuating over the time (changed RF conditions, QRN effects, Out-of-Band effects at the band borders through strong broadcast stations and so on). I need to think about the time interval, how often the value needs to be corrected, so that the pan adapter scaling doesn't become too twitchy. So it is possible that I will make some changes later. This now is the first step, because this was more than one feature request from some users, if I can implement this function.

73 Heiko, DL1BZ