Hello Wahhab, If I recall correctly, you can *not* change the bandwidth of SBX (always 40MHz), and the sampling rate of the USRP2 (always 100MS/s). What you are actually setting by setting --rate 2e6 is the decimation ratio. The signals will be always sampled at 100MS/s, and then decimated by the decimator within the FPGA.
It is still possible to cause aliasing - one way is to just sample at a fast sampling rate and then decimate by yourself. An other way would be tinkering the digital filters used by the decimator, but I am not sure if there are good APIs to do that. I am pretty sure that rx_samples_to_file is not suitable for the task, though (correct me if I am wrong). That is just an example program. Regards, Kyeong Su Shin On Thu, Dec 28, 2017 at 6:29 PM, Wahhab Albazrqaoe via USRP-users < [email protected]> wrote: > Hi John, > Thank you for your reply. > We would like to create aliasing. This means that we should set ADC to > sample at speed less than Nyquist rate. > In our setting, we target RF front end to be 50MHz and ADC speed is 2MHz. > The question is how to do it? We use some commands (as shown in my > previous email) but seems not working as expected, i.e. RF front end > bandwidth is still 2MHz. > > Best, > > On Thu, Dec 28, 2017 at 9:24 PM, John Shields <[email protected]> > wrote: > >> Hi Wahhab, >> This is a fairly basic issue – the ‘bandwidth’ (if >> that is really what you are really meaning) is related to the sample_rate >> by The Nyquist Frequency >> >> https://en.wikipedia.org/wiki/ >> Nyquist_frequency >> >> Kind Regards, >> >> John >> >> *From:* Wahhab Albazrqaoe via USRP-users <[email protected]> >> *Sent:* Friday, December 29, 2017 3:04 PM >> *To:* [email protected] >> *Subject:* [USRP-users] Enable aliasing using USRP >> >> Dear All, >> I have question about how to create aliasing using USRP. >> Basically, I have USRP2 with SBX (with recent installations of GnuRadio >> and UHD). >> I would like to set the bandwidth of the RF front end to 50 MHz, and use >> 2MHz of sampling rate (ADC speed). >> I am using the following command: >> sudo ./rx_samples_to_file --args addr=192.168.10.2 master_clock_rate=50e6 >> --freq=2460e6 --bw=50e6 --rate 2e6 --gain=50 --wirefmt sc8 --nsamps 0 >> >> >> >> Problem: it seems to me that the system (GnuRadio/USRP) observes only >> 2MHz of RF front end bandwdith. How do I know this? Ans: I compare such >> settings with the following settings: >> sudo ./rx_samples_to_file --args addr=192.168.10.2 master_clock_rate=50e6 >> --freq=2460e6 --bw=50e6 --rate 50e6 --gain=50 --wirefmt sc8 --nsamps 0 >> >> The later setting seems to be actual 50 MHz of Rf front end. >> >> Any comments and advices on how to create aliasing using USRP are >> appreciate. >> >> Best, >> Wahhab >> >> >> >> ------------------------------ >> _______________________________________________ >> USRP-users mailing list >> [email protected] >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >> >> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> >> Virus-free. >> www.avast.com >> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> >> <#m_-1409356437401843074_m_5211752623429318912_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >> > > > _______________________________________________ > USRP-users mailing list > [email protected] > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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