http://arrrrv3dzzoluxubt3p24lpn7qu4rxuem3fb4kcmboji3dgpkgt4b2ad.onion/worter/rtl-sdr
I prefer a more automatic approach using GSM channels and kalibrate-rtl . First, use `rtl_test -p` to get a ballpark estimate of the ppm. Let it run a few minutes so the device warms up and you get a more reliable in-use measurement. $ rtl_test -p
Found 1 device(s):
0: Generic, RTL2832U, SN: 77771111153705700
Using device 0: Generic RTL2832U
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4...