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Irregular output #3
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You're using the -rtl version, which are usually cheap / inaccurate devices. You need to do a general tuning to something like a local FM station, before using kalibrate with the Original kalibrate worked well for things like USRP1, which was documented as:
The rtl version is off by a lot more. My rtl dongle is PPM of -743 for example. Without the initial correction (of -730), it picked up wrong GSM channels which resulted in suggested PPM of either 39 or -20. With the correction, it gets within 0.5 PPM between those channels. |
I started a different project for large offsets. If you want to get an initial estimate that works up to ~1000PPM, you can check out https://github.com/viraptor/fm_tune |
As stated, output varies too much channels and modes, for instance, when calibrated against #998 (E-GSM-900), the determined clock error is 11.787 PPM, but when calibrated against steve-m#29 (GSM-900) the determined clock error is 29.680, and #85 yields -0.126 PPM.
Multiple calibrations against the same channel yield consistent results, so why don't multiple calibrations against different channels?
I noticed that someone also mentioned this problem on the kalibrate-hackrf tracker, so while radio implementation is technically possible, software issues seem more likely.
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