Hi usrp-users, I've noticed something strange with an experiment I've been doing. The experiment is set up like a reflectometer. I'm using an X310 with a UBX-160 for transmit and both channels of a TwinRX for receive. In short, I put up a tone with the transmitter by applying a DC offset, tune to a nearby frequency with the receiver (in this case, tuned 50KHz away) and measure the tone. The problem is that the tone isn't being observed at the expected frequency on the receiver.
The data with which I noticed it is in the table below, where I was only using a 2^17 point FFT (763Hz resolution) freq target bin/freq actual bin/freq diff bin/freq dsp freq discrepancy 60MHz 65.536 (50e3) 64 (48,828) 1.536 (763) 1160 397 61MHz 65.536 (50e3) 66 (50,354) -0.464 (-354) -61 415 62MHz 65.536 (50e3) 67 (51,117) -1.464 (-1,117) -1282 165 63MHz 65.536 (50e3) 69 (52,643) -3.464 (-2,643) -2503 140 64MHz 65.536 (50e3) 70 (53,405) -4.464 (-3,406) -3724 318 65MHz 65.536 (50e3) 72 (54,932) -6.464 (-4,932) -4945 13 66MHz 65.536 (50e3) 58 (44,250) 7.536 (5,750) 6044 294 The discrepancy looks like it could be explained by the radio's claimed "dsp tune" not actually occuring. I ran the test over again with larger FFTs (2^20 points) to see if the noted difference frequency would be closer tot he dsp frequency... freq target bin/freq actual bin/freq diff bin/freq dsp freq discrepancy 60MHz 524.288 (50e3) 512 (48,828) 12.288 (1,172) 1160 12 61MHz 524.288 (50e3) 525 (50,068) -0.712 (-68) -61 -7 62MHz 524.288 (50e3) 538 (51,308) -13.712 (-1,308) -1282 -26 63MHz 524.288 (50e3) 551 (52,547) -26.712 (-2,547) -2503 -44 64MHz 524.288 (50e3) 563 (53,692) -38.712 (-3,692) -3724 32 65MHz 524.288 (50e3) 576 (54,932) -51.712 (-4,932) -4945 13 66MHz 524.288 (50e3) 461 (43,964) 63.288 (6,036) 6044 -8 ... and it was indeed much closer. This suggests that the digital part of the tune isn't occuring. Does anyone have any idea what might cause this issue / is it a known problem / any alternate theories on what might be happening? Relevant infos: USRP X310 * UBX-160 (1 TX channel) * TwinRX (2 RX channel, phase sync, lo sharing) UHD 4.0 Dustin _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com