Ty Rob for the link and the suggestions, We agree completely. I need to offset my LO. You are probably not aware that I am using the C API. I cannot use the C++ constructors for tune_request unless they are exported as C API. I can just use the tune_request_t struct, which has no lo_off member. So, I have to offset my LO manually: uhd_usrp_set_rx_lo_freq(uhd_usrp_handle h, double freq, char *name, size_t channel, double *outfreq) I have everything that I need except the LO name:( To get name I use: uhd_usrp_get_rx_lo_names() That's my problem, right there. It just returns me an empty list of names. No errors either. Why? Without it, I cannot use the uhd_usrp_set_rx_lo_freq:( Unfortunately, gdb is no help in this case. After 10 calls to the /usr/include/c++ files and 7 more calls to boost and preprocessor defines, it just advances to the next source line. Not gdb friendly sources:( I am also looking to export as C API the tune_request(freq, lo_off) C++ constructor. This will mean to change code in uhd, which I will eventually have to, but right now, getting uhd_usrp_get_rx_lo_names() to work, is better:)
BR Nikos On Fri, May 23, 2025 at 4:57 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 2025-05-23 09:49, Rob Kossler wrote: > > Hi Nikos, > Your RF card has 120 MHz bandwidth. The strong tone you see will always > be at the center. But, if your application can tolerate using an > instantaneous bandwidth < 60 MHz, you can use offset tuning as Marcus > mentioned. To do this you simply need to create a tune request with your > desired RF frequency and then specify an LO offset frequency of 30 MHz. > This is all that is needed (again assuming that your bandwidth of interest > is < 60 MHz). This link > <https://dsp.stackexchange.com/questions/30562/large-spike-at-the-center-frequency-when-using-ettus-x310> > discusses the topic. > > Also, if you want to reduce the DC offset, there are calibrations for the > X310 - one of which will mitigate this signal. > Rob > > Just a note that AFAIR, the *RX* DC-offset correction is something that > doesn't require input from the calibration routines--it runs all the time > (if its turned on). > > But phase/amplitude *balance* does require that you run the appropriate > CAL utilities: > > https://files.ettus.com/manual/page_calibration.html > > > > On Fri, May 23, 2025 at 8:11 AM Nikos Balkanas <nbalka...@gmail.com> > wrote: > >> I have implemented the following calls for uhd_usrp_set_rx_lo_freq: >> >> uhd_string_vector_handle names; >> uhd_string_vector_make(&names); >> if ((err = uhd_usrp_get_rx_lo_names(dev[channel], channel, &names))) >> warn(log, "Failed to get lo names (%d). %s.\n", 0, FL, LN, FN, >> err, uhdError(err)); >> if ((err = uhd_string_vector_size(names, &len))) >> warn(log, "Failed to get lo names size (%d). %s.\n",0,FL,LN,FN,err, >> uhdError(err)); >> if (!len) >> { >> error(log, "No lo names found on channel %d.\n", 0, FL, LN, FN, >> channel); >> uhd_string_vector_free(&names); >> return(FAIL); >> } >> uhd_string_vector_free(&names); >> >> The problem is that names always returns 0. This is not right for my >> SBX-120, or any >> daughterboard with a tuner:( This is what i can get from the API. There >> are no LO examples. >> I have seen lo_enable() in c++, but nothing exported to C. What am I >> missing? >> >> TIA >> Nikos >> >> On Fri, May 23, 2025 at 8:12 AM Nikos Balkanas <nbalka...@gmail.com> >> wrote: >> >>> Thx Marcus, >>> >>> For your fast and informative answers. Sorry it took me a while to reply, >>> but I'm still trying to get: >>> tune_request(freq, lo_off) >>> to work in C. >>> My X310 has 2 SBX-120 boards. Using uhd 4.6.0 in Ubuntu 24.04. >>> True about the tuner. Much cheaper and easier to implement it in analog. >>> I am using your FPGA image. Haven't touched it myself, yet. >>> So, the spike is pretty narrow to interfere with my signals, but still >>> messes my power calculations:( >>> I already implemented the integer frequency tuner and working on the low >>> oscillator offset. >>> If you have any pointers about it, feel free to advise. >>> LO is not part of the request_tuner_t struct. It is set independently. >>> Is this the same LO in uhd_usrp_set_rx_lo_freq? >>> If this is the case I can modify it externally:) >>> >>> BR >>> Nikos >>> >>> On Fri, May 23, 2025 at 4:40 AM Marcus D. Leech <patchvonbr...@gmail.com> >>> wrote: >>> >>>> On 2025-05-22 21:31, Nikos Balkanas wrote: >>>> >>>> The spike is very clean to come from outside. >>>> Must be from my X310. My tuner must be adding a signal to the >>>> center frequency. The small artifact at 2 Ghz is probably the tuner not >>>> equilibrating fully. >>>> I recently updated my FPGA image. Is that where the tuner lives? >>>> >>>> You haven't mentioned in this thread which daughtercard you're using. >>>> RF front-ends that use complex-baseband >>>> downconversion suffer from something called "DC-offset", which >>>> produces a spike at 0Hz in the complex spectrum. >>>> The radio block in the standard FPGAs has methods for reducing this, >>>> unless you turn it off. This is a very very >>>> *normal* thing for complex-baseband receiver chains. >>>> >>>> If the algorithms are engaged and working, then there'll still be a >>>> central spike, but *considerably* reduced, and I find that >>>> said spike is usually swamped by external signals, even in radio >>>> astronomy. >>>> >>>> The other method that people use is to use "offset tuning". Where the >>>> tuner is tuned to a different RF frequency, and the >>>> DDC brings your signal of interest down to 0Hz. >>>> >>>> https://files.ettus.com/manual/page_general.html#general_tuning >>>> >>>> The "tuner" is an analog collection of components, including an LO >>>> generator, and mixers. While it is *controlled* through >>>> the FPGA, it is an analog subsystem. >>>> >>>> >>>> >>>> On Fri, May 23, 2025 at 3:19 AM Nikos Balkanas <nbalka...@gmail.com> >>>> wrote: >>>> >>>>> Hello, >>>>> >>>>> Whenever I look at my spectrum I always see an energy spike at the >>>>> center frequency. >>>>> In the first image you can see a spike at 2, but not at 2.001 Ghz. In >>>>> the next image, >>>>> at 2.001 Ghz you can see the energy spike at the center frequency, >>>>> but also a small >>>>> spike at 2 Ghz. >>>>> I have verified these results by both fosphor (OpenCL fft) and fftw3f. >>>>> Besides, if it were >>>>> an fft artifact, why is the spike at 2 Ghz still visible after a few >>>>> mins? These spikes >>>>> seem to be transient, but real. In that part of the spectrum, you >>>>> there is no traffic. Could it be harmonics from my power supply? Problems >>>>> with my X-310? My transmitter >>>>> doing funny things (I have 2 boards and not enabling my transmitter >>>>> anywhere)? >>>>> Naming of images is freq_sr.jpg. All are in Mhz. >>>>> >>>>> TIA >>>>> Nikos >>>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list -- usrp-users@lists.ettus.com >>>> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list -- usrp-users@lists.ettus.com >>>> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >>>> >>> _______________________________________________ >> USRP-users mailing list -- usrp-users@lists.ettus.com >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >> > >
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