Fine calibration using GSM network.

- IMPORTANT. Once connected, let it warm up for some minutes (10-20 minutes approx.) to reach its steady state operating temperature.

- Open terminal window and type rtl_test -p

- Write down the maximum supported gain value. In my case 49.6.

- Wait for the cumulative ppm value to stabilize and write down it too. In my case 69.

- Close terminal window

- Open a new terminal and type kal -s GSM900 -g 49.6 -e 69. Replace values in red by yours (GSM850: North America and Western South America. GSM900: Rest of the world).

- Wait for the system to check the band and write down the strongest channel (power). In my case channel 8.

- Now type kal -c 8 -g 49.6 -e 69.

- Wait for the system to check the channel and write down the average absolute error. In my case 63.247. This is my final ppm value!

- On opencpn plugin rtl-sdr, fill in the Error Correction field with your rounded ppm value. In my case 63. Activate and start receiving AIS signal.