Ok, I see.  Yes, get_rssi does just what Rich says--it treats the byte as signed and expands it to 16 bits.  It then subtracts 64 to get the correct RSSI value.  But then it adds 255 to ensure that the value is a positive unsigned value which it can send via telemetry.  Then FoxTelem (which can once again deal with negative numbers) subtracts off the 255 to again get the value that Rich described. 

The console command "get rssi" also subtracts off the 255 and should give the same number that FoxTelem would if we were using it.

73,

Burns Fisher, WB1FJ

AMSAT(R) Engineering -- Flight Software

On Fri, Apr 28, 2023 at 3:58 PM Burns Fisher (AMSAT) <wb1fj@fisher.cc> wrote:

Yes, I think get_rssi does some of that and then -255 does the rest, but it also involves converting from 8 to 16 bits and back, so I need to think about it.

73,

Burns Fisher, WB1FJ

AMSAT(R) Engineering -- Flight Software

On Fri, Apr 28, 2023 at 3:56 PM Rich Gopstein via pacsat-dev <pacsat-dev@amsat.org> wrote:

This was from an old email to Burns:

I found this on the ONSEMI forums:

AX-RadioLAB code sets the RSSIREFERENCE 64 dB (called RSSIOFFSET) higher than the correct value and then subtracts 64 dB when reading out the RSSI value. (And also corrects RSSIABSTHR by 64). This is to prevent wrap around at -128 dBm, since the RSSI register is only 8 bit.

So, it sounds like we're seeing the RSSI as 64dB higher than it really is... 

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