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I am transmitting a 16khz data signal using OFDM 16-QAM x 6 carriers and the library amodem using a HackRF. However, I am having issues receiving this signal as the frequency the HackRF transmits on does not match the actual frequency, and the offset is not static.

I want to find the peak of this transmitted data signal through a given start and end frequency range and decode it. I think the best approach to do this would to be to "center" the HackRF on the peak of the signal through a given start and end frequency range. For example, if I was transmitting the data on 451 mhz, and my frequency range was 450mhz and 452mhz, I want GNU radio to automatically set the HackRF's frequency to 451mhz and "lock on" to the data signal.

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  • $\begingroup$ Hi! Again, that's possible, yes, but it sounds like an XY Problem, and while it may take some work to get this done, I'm not convinced it will actually solve the problem you're trying to solve here. Could you tell us more about the signal, and why you want to do what you're describing? $\endgroup$ – Marcus Müller Jul 20 '20 at 6:13
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    $\begingroup$ @MarcusMüller The issue I have right now is that I'm trying to transmit a 16khz data signal using a HackRF, however there is just too much offset between the frequency I'm transmitting on versus the actual frequency, Also, I want to make sure that the HackRF is in the exact middle of the frequency so there is no issue with decoding the audio. I think finding the peak and "locking on" to the center of that frequency within a given start and end frequency range would be the best approach to do this. $\endgroup$ – Aiden Kaiser Jul 20 '20 at 14:03
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    $\begingroup$ Ah! The classical frequency synchronization problem! There's many established solutions to that, but they all kind of depend of the way you modulate your 16 kHz data signal. Could you elaborate on that (also: add all this to the question, instead of just as comment – that would make it more likely for people to see!). $\endgroup$ – Marcus Müller Jul 20 '20 at 14:07
  • $\begingroup$ I am using 16-QAM x 6 carriers and the library amodem (github.com/romanz/amodem) to modulate data into audio. I also revised my question to match the problem better. @MarcusMüller $\endgroup$ – Aiden Kaiser Jul 20 '20 at 14:18
  • $\begingroup$ ha, nice! A multicarrier systems! nice! 16-QAM isn't very easy to lock onto, but we can certainly think of tricks to use the multicarrier structure to ease that. What's the pulse shape of your carriers? $\endgroup$ – Marcus Müller Jul 20 '20 at 14:42

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