My dongles drift about 8ppm from cold start to warm up after around 40 minutes.
And converter will drift also.
Kalibrate, or kal, can scan for GSM base stations in a given frequency band and can use those GSM base stations to calculate the local oscillator frequency offset.
Download it from here:
See the list of options below.
(I have the ‘Kalibrate’ files on my D: drive in the folder named ‘Kalibrate’)
(The commands below are what are in my shortcuts. If you want to run from a DOS window, just enter everything after the ‘C:\Windows\System32\cmd.exe /k’)
Use this command to find a GSM850 signal in your area.
C:\Windows\System32\cmd.exe /k “D:\Kalibrate\kal.exe” -g 42 -e 22 -s 850
Then, once you have identified a GSM signal in your area, run calibrate using the command below.
C:\Windows\System32\cmd.exe /k “D:\Kalibrate\kal.exe” -e 41 -c 234 -v
For the above command:
GSM Channel 234 (-c 234)
-e is roughly the error rate expected. ’41’ in this case. (not real critical) (-e 41)
That will give you the:
‘Frequency correction (ppm)
Where options are:
-s band to scan (GSM850, GSM900, EGSM, DCS, PCS)
-f frequency of nearby GSM base station
-c channel of nearby GSM base station
-b band indicator (GSM850, GSM900, EGSM, DCS, PCS)
-R side A (0) or B (1), defaults to B
-A antenna TX/RX (0) or RX2 (1), defaults to RX2
-g gain as % of range, defaults to 45%
-F FPGA master clock frequency, defaults to 52MHz
-D enable debug messages
Then, if you are using a converter, you need to set ‘Shift’ or ‘Offset’ for it.
I don’t use a converter so I can’t help with that part.
If you have ‘Snap to grid’ selected, SDRSharp will land on an exact multiple of your selected step size.
Using channel 136, the ‘Frequency correction offset’ rounds up to 38ppm. (SDRSharp accepts whole numbers only)
Source : Extracted from forums.radioreference.com