2017-09-15, 09:05 PM
I think calibration software is working right.
Cheap dongles have bigger variation with temperature. Connect your dongle for 1 or 2 hours and then calibrate.
The ppm tolerance is +/-7 ppm.
OP calibration method is based on GSM stations and is quite accurate. You need a visual confirmation of your calibration with gqrx or "take a look button".
There is another method, disable AIS reception, open a terminal and type "rtl_test -p" you will get something like this every 10 seconds:
real sample rate: 2048184 current PPM: 90 cumulative PPM: 90
run this for hours until the PPM value stabilizes.
Cheap dongles have bigger variation with temperature. Connect your dongle for 1 or 2 hours and then calibrate.
The ppm tolerance is +/-7 ppm.
OP calibration method is based on GSM stations and is quite accurate. You need a visual confirmation of your calibration with gqrx or "take a look button".
There is another method, disable AIS reception, open a terminal and type "rtl_test -p" you will get something like this every 10 seconds:
real sample rate: 2048184 current PPM: 90 cumulative PPM: 90
run this for hours until the PPM value stabilizes.