Thanks Clint and Marcus for your help. I clarified my concepts.
Regards Isaac T. El mar, 11 may 2021 a las 20:26, Clint Scarborough (< clinton.scarboro...@gmail.com>) escribió: > Hi Isaac! > > Your questions are really general signal processing questions, or at least > GNURadio questions, not unique to a USRP. I was confused on the same > subject when I first started using SDRs, though. > > Nyquist really just means that, if you have a real signal with no power > outside a given bandwidth (let's say 20MHz), then you need 40 million > independent samples per second to represent it. You can get that by > real-valued sampling using a regular clock at 40Msps, or you can > simultaneously sample in-phase and quadrature components at 20Msps yielding > complex valued samples. The latter approach is what you'll generally find > with SDRs. > > However, if you want to accurately represent your 20MHz signal digitally, > you need a bandpass filter in front of the analog to digital converters > with a 20MHz pass band. Any real filter will have some rolloff at the band > edges, which means that your signal may have power beyond the 20MHz that > you care about, and you need a little higher sampling rate to avoid > aliasing of that extra power. > > Secondly, the sampling has a limited number of bits to represent the > analog signal, and you need a slightly higher sampling rate to guarantee an > accurate representation of your signal. > > So, with complex sampling, you generally need to sample at roughly the > same rate as the bandwidth you care about plus maybe 25%. > > -- Clint > > On May 11, 2021 6:15:26 PM EDT, isaac mario tupac davila < > isacct...@gmail.com> wrote: >> >> Hello community >> >> I'm Isaac. I'm dealing with some questions about the interpretation of >> sampling rate and bandwidth in a USRP source block. >> >> What I understand is if I work with an USRP N210, my ADC works with a >> 100MS/s. If I use a Gigabit Ethernet and a data type of 16bits, I could >> receive in my host up to 25MS/s with a bandwidth of 20MHz. >> https://kb.ettus.com/About_USRP_Bandwidths_and_Sampling_Rates >> >> My questions are: >> >> 1. If I can receive up to 25MS/s on my host, why my bandwidth is 20MHz? I >> think It is up to 12.5MHz according to Nyquist. >> >> 2. Why is the sample rate value in the usrp source block equal to the >> bandwidth I observe? I think this bandwidth should be the half according to >> Nyquist too. https://wiki.gnuradio.org/index.php/USRP_Source >> >> I appreciate any help to clarify this concepts >> >> Regards >> Isaac T. >> >>
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