Hi Marcus, thanks for the sketch; for the next time, screenshots are best done by > using GRC's "Screen Capture" functionality, or at least with your operating > system's screenshot function. Can't be that hard. > > Not at all! Sorry, I was taking pictures of hardware and hence just took one for the GRC too. As I showed in previous picture, I am only using RX-B. I am not sure how to connections will be for dual mode, but currently I am just using one. I get complex values in the GRC and I can plot complex FFT of them.
My sample rate is 400 KHz and my center frequency is 200 KHz. GRC 1] : http://postimg.org/image/6653d0rm9/ What is the rough line? Why did you chose to photograph a reflective > surface agains daylight? > > I have a better picture[2] now : http://postimg.org/image/hptdrl2vl/ > And, as I mentioned in IRC when I asked for them, it is important to > define wheter you're doing I&Q or real sampling. > I am dong I&Q sampling as shown in [1]. By real sampling, I suppose you meant that I am taking magnitude before feeding to the Spectrogram. > It's no use discussing any of your question until we know whether we're > looking at a complex equivalent baseband or at a real signal. > > I am doing complex baseband as in the picture. My question was related to the sampling. I thought doing sampling (complex baseband as shown in GRC) in 250kHz at center frequency 125kHz is equavelent to doing 500kHz, with center frequency 0Hz using LFRX. In 0 Hz case, I wasn't able to make of the negative frequency (apart from the artifact that they are in opposite direction, I read in books). I think I am not clear in my understanding, so I wanted to ask someone knowleagable. Thank you for your time, Abhinav Best regards, > Marcus > > > > On 27.04.2016 19:13, abhinav narain wrote: > > Hi all, > I want to sample first 250KHz on the channel. > I am using the (sampling_with_lowpass.JPG) setup to extract quadrature > samples. > I have LFRX card where i just use the RX-B pin to extract complex samples > from the channel. > > My question is (question.JPG) how are the two setups different, assuming > the connections are correctly made. > > a) I set the sample rate= 250KHz, and center freq=125KHz. > b) I set the sample rate=500KHz, and center freq= 0 KHz (I hope the card > is fine with setting center freq=0) > > Q1 ) I understand that the sampling rate will be different, but I should > be getting the samples from same bandwidth ? 0-250KHz > > Q2 ) in b), how do i interpret the negative frequencies in complex FFT. > ( I understand these are frequency in opposite direction acc to books, but > not sure if they make sense here, and hence I am doing way a) ) > > Apologies, I am CS student so I might not be very clear with my EE > fundamentals. > Thanks, > Abhinav > > > LFTX setup- http://postimg.org/image/9s6hy4rqp/ > sampling_with_lowpass - http://postimg.org/image/qkpeeqgz5/ > question - http://postimg.org/image/3mjsmwcc1/ > > > > _______________________________________________ > 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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