[aprssig] GiSTEQ Explorer

[Scott Miller]

On another quasi-APRS subject, someone was nice enough to loan me one of 
these:

http://www.gisteq.com/Explorer.php

As far as GPS functions go, it looks like a clone of an older Garmin 
model, like maybe the yellow eTrex or a GPS III with no mapping capability.

It has burst-after-voice and SOS capability, and allows transmission of 
waypoints and text messages.

The bad news is that there's no obvious way to adapt the hardware for 
APRS use.  It uses a CML Micro CMX469A modem in 1200 baud MSK mode with 
1200/1800 hz tones.  Unless CML happens to make a pin-compatible Bell 
202 chip, or there's a DAC and ADC connection to the processor that I 
haven't found yet, it's never going to interoperate directly with APRS.

(Hmmm.. unless one could wedge a little board in there to replace the 
modem chip and translate packets on the fly... but it'd be a damned 
expensive APRS gadget, even before the modification.)

No luck so far on decoding the actual data, but it doesn't look like 
it's using a scrambler or bit stuffing - too many long runs of 1s or 0s. 
  I've tried MSB/LSB first and both polarity possibilities, plus 
differential encoding, and haven't gotten anything recognizable yet.  I 
need to grab a few more packet samples with different data to compare.

Scott
N1VG