Small collection of scripts used to automate starting and calibrating PPM for running Direwolf on my Raspberry Pi.

Problem: RTL-SDR sticks the PPM varies as the temperature changes, and decoding APRS requires the PPM to be pretty close, probably within 2-3 or you'll have issues decoding.

Solution: Using NOAA1 as a source, I use rtl_power to find the best signal and then figure out what the correct PPM is based on that, and use that new PPM.

I have a cron which runs the dw-start script every 5 minutes (in case the Pi has rebooted, etc) and once an hour (at the 00 minute mark) this startup script will run the calibration. Other runs will use the last calibration determined which is output to a file which is sourced at the top to be used.

Files:

• dw-start - Script which is ran every 5 minutes
• findppm.pl - Perl script which determines the best PPM
• direwolf.sh - Script which actually starts direwolf

Each script is commented and hopefully clear what they each are doing. I hope this is useful for someone else. What this repo is NOT is a stand-alone thing, but perhaps in the future I'll add a little more and enhance it be more of a one-stop way to get Direwolf using an RTL-SDR up on a Raspberry Pi.