You might also want to check out Jeff Long's presentation on sampling rate at the GRCon15 Intro Day:
http://www.trondeau.com/grcon15-presentations#monday_Long_Sampling Video: https://www.youtube.com/watch?v=AmY7fCGTKs4 Tom On Wed, Sep 16, 2015 at 5:57 AM, Marcus Müller <marcus.muel...@ettus.com> wrote: > Hi Gerome, > > I hope the subject I've added suits the topic of your mail well; if not, > feel free to change it when replying)! It's kind of important to have a > proper subject line, as it'll allow people to directly address your mails. > > What does the sampling rate in this usrp block does? > > It sets the sampling rate of the stream of samples coming from the USRP. > > Is this the one that samples the IF from my TVRX2 daughterboard? > > It's the sampling rate that the 100MS/s from the ADC get decimated to. For > example, you can set a 10MS/s sampling rate, and the USRP will internally > take the 100MS/s from the ADC, and filter them down to 10MHz and decimate > to 1/10th of the original rate. > The TVRX2 is a bit special compared to all other daughterboards because it > actually uses a real IF, all other daughterboards are direct converters > that give complex baseband. The samples that the USRP sends to the host are > all "pseudo-complex", ie. (sample_value + j*0). > > Or is this the bandwidth that is displayed on the QT Sink? > > No, not inherently: You can configure any "sampling rate" parameter in the > QT Sinks, and that will do nothing but change the numbers on the frequency > axis. It doesn't have an effect on the signal, just on the labeling. > > I'm asking this because whenver I set it to say 400 kHz in sampling rate, > it give me a bandwidth of 400 kHz. > > Not quite sure about that: As the TVRX2 is a 2x real IF device, the USRP's > FPGA is configured to give you a real sample stream -- meaning that the > 400kS/s are real samples, and that the bandwidth would be 200kHz. > For all IQ-demodulating direct conversion daughterboards (ie. everything > but TVRX, TVRX2, BasicRX/TX and LFRX/TX) you get complex sampling, where > f_sample == b_nyquist, but for real signals, Nyquist dictates that the > representable bandwidth is half the sampling rate, remember? > > If this sets the sampling rate in the usrp, it should only make the plot > nicier, not increase its bandwidth. If I am not mistaken. > Thanks in advance. > > I don't understand -- obviously, increasing the sampling rate will > increase the bandwidth of a digital signal. That's the mathematical effect > of sampling. > However, the TVRX2 is among the very few daughterboards with adjustable > analog bandwidth -- you can select between 1.7 MHz, 6 MHz, 7 MHz, 8 MHz and > 10 MHz of analog filter bandwidth. > > Best regards, > Marcus > > On 15.09.2015 18:11, Gerome Jan L wrote: > > Hi guys, > > What does the sampling rate in this usrp block does?i'm talking about the > uhd:usrp source block. Is this the one that samples the IF from my TVRX2 > daughterboard? Or is this the bandwidth that is displayed on the QT Sink? > Or is this the bandwidth that needs to be sample. As far as I know, > sampling rate is fixed at 100 MSps by the ADC. > I'm asking this because whenver I set it to say 400 kHz in sampling rate, > it give me a bandwidth of 400 kHz. If I increase does, it increases the > bandwidth too. If this sets the sampling rate in the usrp, it should only > make the plot nicier, not increase its bandwidth. If I am not mistaken. > Thanks in advance. > > > -- > > Best, > > *Gerome Jan M. Llames * > Aspiring Technopreneur | Tech Savvy | Curious > Mobile: +639271525124 > Email: <geromejanlla...@gmail.com>geromejanlla...@gmail.com > > "*Because the people who are crazy enough to think they can change the > world, are the ones who do.*" - Steve Jobs > > > > > > _______________________________________________ > 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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