[aprssig] APRS Speed Spec? (Above Mach 1)
bruninga at usna.edu
Thu Oct 12 09:16:26 EDT 2017
In a move to keep APRS relevant, there was some useful feedback on the idea
to extend the speed range of APRS reporting. I like the transition at Mach
1 (670 kts).
So here is the way to handle speeds above Mach 1 and it works for both MicE
and CSE/SPD values of X speed field.
If X Less than or equal to 670 then SPEED = X in Kts
If X is greater than 670 then SPEED is 135X -90000 in Kts
You do not even need to do the math. You can just use some pre-calculated
values shown here:
779 = 15,200 knots space station
682 = 2100 knots Mach 3
678 = 1600 knots military
677 = 1340 knots Mach 2
675 = 1200 knots Concorde
670 = 670 knots Mach 1
These remain in Knots because that is the APRS standard for speed, but of
course you can also display them in MPH if you want to make that conversion
which I think all PILOTS use.
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