Hi Abhinav, I think most of your questions have been answered in my reply to your reply to Sylvain's mail; basically, yes, you need to use a sampling rate >=196kHz, but no one is stopping you from putting any signal into that sampling rate that has a smaller bandwidth. See my comments on oversampling.
Best regards, Marcus On 10/21/2015 08:37 PM, abhinav narain wrote: > > Hi Marcus, > > On Wed, Oct 21, 2015 at 3:18 AM, Marcus Müller > <[email protected] <mailto:[email protected]>> wrote: > > Hi Abhinav, > > which USRP are you using? > > USRP N210 > > > I'm pretty sure none of our devices supports a 2kS/s sampling rate > -- it's just far too low to get directly interpolated to a > "usable" DAC/ADC rate. Especially those USRPs that can be equipped > with RF frontends (daughterboards) that can operate at > near-baseband (400kHz) shouldn't be able to work at such low > rates. So: which daughterboard are you using? > > I see your point, I am using Basic TX/RX daughterboard. > I didn't notice the shell output but it makes sense now : > > Terminal output: > The hardware does not support the requested TX sample rate: > Target sample rate: 0.001000 MSps > Actual sample rate: 0.195312 MSps > -- Tune Request: 0.400000 MHz > -- The RF LO does not support the requested frequency: > -- Requested LO Frequency: 0.400000 MHz > -- RF LO Result: 0.000000 MHz > -- Attempted to use the DSP to reach the requested frequency: > -- Desired DSP Frequency: 0.400000 MHz > -- DSP Result: 0.400000 MHz > -- Successfully tuned to 0.400000 MHz > > > Basically, the minimum sampling rate is 196 Ksamples/sec > > Hence, UHD should have told you that you can't use that sampling > rate, and a higher sampling rate was automatically selected, > inherently frequency-"stretching" the signal by the ratio of > (actual rate/2kHz). > > You should heed Sylvain's advice. Just oversample your signal by > using an interpolating FIR filter to something that the USRP can > happily work with. > > So, here is what I am not clear about- I should use 196 KHz as > sampling rate ? > So, the minimum BW of my signal will 196/2 =98KHz, and that is the > best I can do with this equipment, right ? > > > > > > Best regards, > Marcus > > On 21.10.2015 08:49, abhinav narain wrote: >> Hi, >> I am transmitting using the flowgraph: vector src-> FIR >> interpolator (with RRC filter as below) -> MultiplyConst -> USRP >> Block >> >> FIR filter - firdes.root_raised_cosine(32, samp_rate, sps, 0.55, >> int(11*sps*32)), with >> center freq= 400kHz >> samp_rate= 1k >> >> I am listening using other USRP with >> center freq= 400kHz >> samp_rate= 2k >> >> >> You can see the spectrogram at the receiver. I want to do >> narrowband(1 kHz) transmission hence I am keeping the sampling >> freq at transmitter at 1k. >> >> While I increase the signal amplitude(using MultiplyConst block >> with slider), I see there is more and more spillage of energy in >> the neighboring frequencies! >> >> Is there a way to remove that spillage from the transmitter and >> have a cleaner transmitter ? >> If not, how can I atleast mitigate it to the minimum ? is there >> something I can do with RRC filter parameter or any other way ? >> >> In the figure: 1 - when amplitude is large; 2 - when amplitude is >> turned down >> >> Thanks, >> Abhinav >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] <mailto:[email protected]> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] <mailto:[email protected]> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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