[aprssig] ARPS physical layer

[Curt, WE7U]

There's a byte-wise CRC16 algorithm that was published in an IEEE
magazine in the late 70's or early 80's that I used when I wrote
assembly for decoding packets in '84 or '85.  Worth checking out if
you're writing code.

-- 
Curt, WE7U.                         <http://www.eskimo.com/~archer>
    APRS:  Where it's at!                    <http://www.xastir.org>
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