[aprssig] ARPS physical layer

[Scott Miller]

> The references to a data scrambler you found are probably for the 9600
> bps G3RUH variant. The 1200 bps "regular" packet doesn't use a
> scrambler, if you don't count the bit stuffing required to keep HDLC
> flags unambiguous as a scrambler.

And if anyone knows the details of the G3RUH preamble, let me know. 
I've had a heck of a time finding it.

Scott
N1VG