Hi! If you experience strong distortions in your signal, then this could be related to the cic interpolator and decimator in the usrp. I am transmitting ofdm signals. When those signals occupy the whole sample bandwidth, or a greater part of it, the frequency band at the border is greatly attenuated. Especially when the complete bandwidth is used (i.e. in your case 8 Mhz), the received signal looks similar to a gaussian distribution.
At the moment, I bypass this problem by using filters on transmission and receiving side. They interpolate/decimate by a constant factor, for example 2x. The data rate sent to usrp is therefore doubled. To test the filter and run some experiments, I have modified usrp_fft.py and usrp_siggen.py. Maybe you want to have a look at these. My hardware are two usrp's, revision 4.2, with Flex2400 daughterboard installed. Greetings Dominik
patch_usrp_utils.tar.gz
Description: application/compressed-tar
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