Hi Anon, thanks for this explanation. Just a thing: so if I understand well, my "new" 0 is 97.5mhz. Why if I'm filtering at 75khz (cutoff freq) and so 97.5mhz+75khz, I can see the other higher/lower frequencies on the fft sink? a filter should brutally cut the frequencies after the "cutoff freq" thanks a lot
Matteo 2018-05-09 12:32 GMT+02:00 Anon Lister <listera...@gmail.com>: > At that point they do not. > > Hackrf's job is to take energy at a desired frequency, say a 200khz > broadcast radio station at 97.5mhz and down convert it to a 200khz wide > station spanning -100khz,100khz. > > However, the hackrf doesn't work best when running at exactly 200khz > sampling rate. It likes higher sampling rates. So you sample at say > 8Msample, and bring down 97.5-4, 97.5+4. > > But now you have a problem, the energy you are listening to (centered at > 0,) will have many higher frequency components that got pulled in with that > 8M span the hackrf brought down. So a low pass filter will remove that > unwanted extra stuff from both sides. > > At this point the data can be resampled, and demodded. > > On Tue, May 8, 2018, 09:00 Matteo Terzi <matteo.terz...@gmail.com> wrote: > >> Hi all, >> I'd like to know why does Micheal Ossmann use a Low Pass Filter in the >> Lesson 1 (https://greatscottgadgets.com/sdr/1/ --> minute 22:00). >> He says that in that way just frequencies near to the zero Hz can pass >> but it doesn't make sense....how radio frequencies can pass if they have a >> value of MHz?? >> Thanks >> >> Matteo >> >> -- >> Matteo TERZI >> Google Gmail Member >> _______________________________________________ >> HackRF-dev mailing list >> HackRF-dev@greatscottgadgets.com >> https://pairlist9.pair.net/mailman/listinfo/hackrf-dev >> > -- Matteo TERZI Google Gmail Member
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