Fix RSSI display value

[helioz2000]

The S part of the RSSI display value is wrong and does not match the dBm value shown next to it. For example -23dBm displays as S9+70dB, the correct S meter value for -23dBm is S9+50dB since the signal is 50dB above S9 (-73dBm). (https://en.wikipedia.org/wiki/S_meter).

Here is an example illustrating the wrong S display:

Same display with corrected code:

[MW0MWZ]

The S-Meter calibration is correct, please read here: http://www.rfcec.com/RFCEC/Section-3%20-%20Fundamentals%20of%20RF%20Communication-Electronics/33%20-%20TRANSCEIVER/Transceiver%20-%20S-Meter%20Calibration%20&%20IARU%20Standards%20%28By%20Larry%20E.%20Gugle%20K4RFE%29.pdf

Remember we are calibrating for VHF/UHF, and these values are 20dB different from HF (this is what you are suggesting).

[helioz2000]

Thanks Andy,
of course, you are 100% correct.

However here is a point for discussion/consideration:

Back in 1981, when the IARU technical recommendation was published, digital modes had not been invented and noise floors may have been much lower. These days I expect an average noise floor to be -110dBm on a good site. Most sites I have measured are more like -95 or -100dBm. And I'm not alone with this experience: https://www.linkedin.com/pulse/vhf-dead-joe-blaschka-jr-
Also Table 2 in this publication: https://www.radioworld.com/news-and-business/noise-floor-where-do-we-go-from-here

I'm not sure what other user experience is, but I find lots of 9+XX signal reports on the dashboard, even for distant/mobile stations, some signals go down as low as S7 but then disappear completely below S6/S5 .
This is somewhat misleading as I would expect a station with S7 had some margin left before dropping out, but in practice, if the station drops another S point or two it can no longer be received.

It is my view, that, in the context of digital systems such as pi-star, the VHF/UHF calibration scale renders the bottom part of the S-scale (S1-S5) completely useless since stations below -117dBm (S5) can not be received as they are below the noise floor.

I would not argue with the IARU VHF/UHF scale recommendation as I'm sure the authors had a technical/theoretical reason, but I can see no valid reason to calibrate an S-Meter to accommodate signals below -120dBm when we are unable to receive such signals in the real world we operate in.
Hence I would argue that the pi-star community would greatly benefit from using a more realistic and meaningful signal scale.
The IARU HF scale assigns S1 to -121dBm which is about the noise floor on a good site, so it seems a much more appropriate solution for our purpose and more representative of when we can expect to loose a signal.

[AndyTaylorTweet]

The other option is to calibrate the RSSI dat file differently, we always try to be "correct" - however I do agree with you in as much as I also see the same behaviour, its either full scale, or there is no signal :(