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proto17 / dji_droneid

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the problem of frequency_offset #40

Open Dream190802 opened 1 year ago

Dream190802 commented 1 year ago

Hi, in the file of processfile.m , there is a frequency offset variable, while also inputting the extract_bursts_from_file function, and you also mentioned in the comment "How far off from DC the signal is in the recording", I would like to know the frequency_offset is the sampling center frequency of SDR? For example, I used USRP for sampling at 2.4445GHz with a bandwidth of 10MHz and frequency_offset is 2.4445GHz. Thank you.

proto17 commented 1 year ago

It's where in the baseband collect that the signal resides. So, if the signal you wanted was at 2.4445GHz and that's what you set your SDR to, then the frequency_offset variable does not apply to you (leave it at 0). However, if your SDR has a really bad LO spike and you had to tune up or down before recording then you will need to use frequency_offset. Example: You have a sampling rate of 30.72e6, and you tuned the SDR to 2.4445 GHz + 15 MHz (2.4595 GHz) then you would use a frequency_offset value of 15e6 (or maybe -15e6, not totally clear to me right now).

Basically the frequency_offset value is there to center the signal in baseband before being processed should there be an offset after the recording. It is not for dealing with very small frequency offsets that just exist in any RF communications as that is handled by the CFO estimation logic.

Dream190802 commented 1 year ago

Thank you very much for your reply. I roughly understand.