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[aprssig] PHG calculation formula?

scott at opentrac.org scott at opentrac.org
Fri Oct 27 16:16:03 UTC 2006

> ... and that's most likely because it isn't one of the operators  
> typically built into hardware.

I consider myself lucky that I have an integer multiplier available in the
chips I use!  It'd be harder to do PSK31 (or audio level control for AFSK)
without it.

The use of exponents in several portions of the APRS spec shows that it
really wasn't designed with embedded hardware in mind.  A calculation that
might be trivial in BASIC on a PC can eat up a large chunk of your code
space on a chip with no native floating point support, using the standard

Though I suppose it's not as much of a pain as Garmin's
position/velocity/time format, with the trig required to convert x/y
velocities to course/speed.  It DOES give you a z (vertical) velocity
component, though - I'm thinking about using that to get a climb rate
indication on my upcoming balloon launch.

Speaking of which, anyone who wants to join us on the morning of Nov. 11 at
Red Rock Canyon State Park in the Mojave desert is welcome to.  We could use
more chasers.


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