Thangaraj, The first thought for your "aU" situation is that your sample rates don't match between your USRP and the audio card on your computer. The "a" part of "aU" means the audio card is not getting enough samples. If you run your Gnu Radio graph, is there a line above all of the "aU"s that says something like, "[WARNING] [MULTI_USRP] The hardware does not support the requested RX sample rate:", followed by a couple of lines that say something like, "Target sample rate: 1.920000 MSps, Actual sample rate: 1.923077 MSps"? If so, then your USRP is not able to *exactly* set the sample rate to 1.92 MHz.
If you are *not* able to set the sample rate of the USRP to precisely 1.92 MHz, try the following changes to your graph (which looks correct from your image): Sample rate: 2e6 (2 MHz) Rational Resampler Block: - Interpolation: 24 - Decimation: 250 Leave all of the other blocks the same. Long story short: If I'm correct, it's because the USRPs can only pick from a small number of sample rates. For the N320, they start with one of three sample rates (200 MHz, 245.76 MHz, and 250 MHz), then they decimate. The sample rate *must* be one of these values after decimation. Otherwise, the USRP will pick something close. And close is not good enough for our purposes. The above information came from the Ettus website at https://kb.ettus.com/N320/N321. If I'm reading it correctly, it *should* be able to set the sample rate of the N320 to precisely 1.92 MHz. Again, assuming I'm reading it correctly. Finally, I agree completely with Barry that your antenna should be more than adequate for the USRP. Best of luck, and please let us know if you're able to solve this problem. Regards, Gary
