I have some questions about FFT method. - I have done a test with my signal ( [Signal] -> [FFT] -> [IFFT] -> [Signal] ) and I have a problem with the spectrum (central lobe):
- To insert a delay I multiply the FFT by [1], right? Can I insert a delay (no variable) if I multiply the FFT by GNURadio sine complex block? Greetings, Carlos Alberto Ruiz Naranjo. Área de Aviónica y Sistemas No Tripulados/Avionics and Unmanned Systems Department Parque Tecnológico y Aeronáutico de Andalucía C/ Wilbur y Orville Wright, 17-19-21 41309 La Rinconada Sevilla (Spain) (+34) 954179002 http://www.catec.aero/ [1] N: length of FFT, m: delay, k: position 2014-11-12 15:32 GMT+01:00 Marcus Müller <marcus.muel...@ettus.com>: > well, yes, you could, but that sounds ugly: > 1. a sample rate of 1e9Hz implies --for complex float-- a memory > consumption of 1e9*8B~=8GB per second... > 2. unwieldy fractional resampling, because 10.23e6 and 1e9 don't have a > very large common divisor; you'll be interpolating by a factor of 100000 > just to decimate by 1023... That is effectively just very very many samples > in-between. > 3. you're sampling at 10.23MS/s, but you want to do something with a > temporal resolution of 10 times that rate; that's a phase shift, for sure, > but I'm afraid that it sounds like you're trying to harm Nyquist in some > way or another. > > When were talking on how to simulate delay introduced by radar range in > GNU Radio, a wise[1] elder[2] told me to do time shifting in frequency > domain: > > The idea is that a time shift corresponds to frequency shift in frequency > domain, so you can, within the spectral precision defined by the length of > your DFT, have arbitrary shifts by doing [time signal]->[DFT]->[multiply > with complex sine]->[IDFT] . Note that, due to the circular nature of the > DFT, this will distort the first samples of the output. > > Greetings, > Marcus > > [1] one might consider him wise > [2] not really an elder > > > On 11/12/2014 02:50 PM, Carlos Alberto Ruiz Naranjo wrote: > > Hello, > > I have in my project a sample rate of 10.23 million samples per second and > I need to delay the signal +-1ns. With GNURadio block delay I can delay the > signal 97.75ns (1 / 10,230,000 -> + - one sample). > > Could I use the fractional resampler block to enter a variable > fractional delay? > Has anyone implemented a fractional delay block? > > Thank you. > > > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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