Greetings! I've been using a USRP B100 (!) for ten years now, writing C code with the UHD API. Recently I upgraded to a B200mini, but the resulting baseband signals from these two USRPs is different, even though I am running the exact same code and API calls in both cases. For the B100, the target frequency to which I tune (with uhd_usrp_set_rx_freq) always appears at 0 Hz in the complex baseband; but for the B200mini, I determined (empirically, with MATLAB) that the target frequency for the examples I tested is mixed not to 0 Hz, but to 3 kHz (?) in the baseband samples. In addition, when I run uhd_fft on the B200mini, I see this same behavior as well: when I tune to a known P25 signal at 860.2375 MHz, in the resulting power spectrum I see the peak appearing at 860.2405 MHz (target + 3 kHz), and I see a notch at the target 860.2375 MHz (in the passband of my signal).
I examined the tune_result structure but it reports the target frequency is 860.2375 MHz, and it reports the target/actual RF frequency is 860.2375 MHz, and the target/actual DSP frequency is 0 MHz. I don't see anything that indicates a "3 kHz" offset. But if I mix the received samples from the B200mini down by 3 kHz, then I do get good decoding with my software. So right now, if I am using the B100, I have no 3 kHz downmix, and if I use the B200mini, I need 3 kHz downmix -- this is weird. Is this a hardware defect, or is this some setting that I have missed? Thank you! Jon Barry _______________________________________________ USRP-users mailing list -- usrp-users@lists.ettus.com To unsubscribe send an email to usrp-users-le...@lists.ettus.com
