Dear Sam, Your shot in the dark hit the bullseye. At 25 MHz, this problem goes away entirely. Will have to work around the limitation at 20 MHz BW in the future.
Thank you very much! Manav On Sun, May 24, 2020 at 12:35 AM Sam Reiter <[email protected]> wrote: > Manav, > > I'll take a shot in the dark and point you toward this article I've > referenced a couple times in the past: > > > https://witestlab.poly.edu/blog/why-does-my-received-spectrum-droop-at-the-edges/ > > In order to decimate data, the USRP will use halfband filters for > decimation factors that are a multiple of 2, and will use a CIC filter for > anything else. The use of this CIC filter causes rolloff similar to what > you're describing. If you change your sample rate to be a decimation factor > of 2 from the MCR and you see an improvement, then you've found the culprit. > > -Sam > > On Sat, May 23, 2020 at 3:08 PM Manav Kohli via USRP-users < > [email protected]> wrote: > >> Setup details: >> USRP N210 w/SBX daugterboard >> UHD 3.14 >> GNU Radio 3.7 >> Ubuntu 16.04 >> gr-digital GNU Radio OFDM blocks used >> >> While attempting channel estimation for 64-subcarrier OFDM, I find that >> for higher bandwidths, such as 20 MHz, the channel estimate shows the edge >> subcarriers anywhere from 15-20dB below the central zero subcarrier, even >> though the anticipated channel is relatively flat. >> >> Taking a larger FFT of the entire received OFDM packets shows the same >> rounding as seen in the channel estimation. This rounding is roughly >> symmetric, and occurs with any carrier frequency used. >> >> It was suggested to me that this may be caused by the antialiasing filter >> on the SBX board, and any further help/advice would be greatly appreciated. >> Is such rounding normal, and if so, how could it be compensated? >> >> Much thanks, >> Manav >> _______________________________________________ >> USRP-users mailing list >> [email protected] >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >
_______________________________________________ USRP-users mailing list [email protected] http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
