Yeah, I know 9361 doesn't support external LO, that's why I am looking into purchasing N320. I am interested in the ability of fast sweeping to do spectrum sensing/monitoring.
I thought about building a custom super-heterodyne front-end and driving it from, say, the GPIO pins of the SDR but looking at Ettus' offerings, N320 seemed promising as a built-in solution. However, from your replies it looks like there are further complications and nuances and it is not as straightforward as I hoped. Best, Temir On Mon, Dec 6, 2021 at 10:28 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 2021-12-06 14:22, Temir Karakurum wrote: > > Hi Marcus, > > Thanks for your prompt response! Your answer is in line with my > expectations. I was mostly wondering how set_rx_freq would interact with an > external LO. Like would the tune_request only allow for DSP tuning whereas > RF tuning would be (hardware) locked within UHD? > > With external LO, would the tune request triggered calibration routines > induce substantial time? I believe for B210/E310 pll lock can be achieved > in a few ms and within 100/150ms after crossing a 100MHz calibration > threshold. Whereas for AD9361 fastlock mode allows for 25 us lock-in time > (there was a demo by Analog Devices using iio in grcon19) and I was looking > into whether fast sweeping could be achieved using an external LO. In a > similar vein can such fast sweeping be achieved using an Ettus > daughterboard driven by an external LO? > > Best, > Temir > > Again, the AD9361 DOES NOT SUPPORT an external LO, which eliminates E3xx > and B2xx devices. > > The whole "fast lock" thing isn't easily achievable if you need your > device to be fully-general, because there are only a few calibration > "cache" slots, and managing that cache from > the host side would be quite complex. > > The X3xx supports the TwinRX series, which can be made to support an > external LO, and there's an article in the KB about exposing the external > LO sharing signals to the > "outside world" on X3xx. > > https://kb.ettus.com/Modifying_an_X310_Chassis_for_External_LO_Sharing > > The "tune_request" objects can be constructed to ONLY tune the DSP logic, > which is fast. So as long as you're staying within the bandwidth of the > ADC, you can fast-hop > within that bandwidth. > > https://files.ettus.com/manual/structuhd__tune__request__t.html > > > > > On Mon, Dec 6, 2021 at 9:58 PM Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 2021-12-06 13:42, Temir Karakurum wrote: >> >> Hi, >> >> I have some experience working with E310 and B210 and one of the >> bottlenecks for my application is the frequency tuning/hopping time of >> AD9361. I understand that N320 has the ability to use an external reference >> oscillator but I am not sure what this actually entails. >> >> Does this mean that the LO used in the homodyne IQ receiver architecture >> is no longer generated by the PLL but is directly supplied by the >> external reference? If so, does this mean that I can sweep the frequencies >> as fast as I can generate LO frequencies in a similar fashion to a swept >> spectrum analyzer? Is external LO mode useful for spectrum >> sensing/frequency hopping applications or is it mostly used for >> applications that requires >> phase coherence? >> >> Also are there any UHD examples or tutorials depicting how to build >> tune_request objects under 'external LO' mode? >> >> Best, >> Temir >> >> External LO is largely about providing phase-coherence. The AD9361 in >> the E310 and B210 has NO support for external LOs, but the AD9371 in the >> N310 does have support >> for a 2XLO. >> >> When you create the multi_usrp device object, you'll pass in an >> "rx_lo_source=external" argument, and make sure the external LO, at that >> moment, is operating at 5GHz. >> Once device initialization has completed, you can >> set_lo_source("external"). See: >> >> >> https://www.gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__source.html#ae24f390fef2a0692dc230a5284ad1002 >> >> Now, how that interacts with future set_rx_freq() or set_tx_freq() I'm >> not clear on. The AD9371 in the N310 must necessarily complete some I/Q >> calibration and compensation >> functions every time it tunes to a new frequency. It's not clear (and >> I cannot find examples) how you can trigger that calibration process after >> you change your external LO. >> >> In any case, the external LO needs to be at *TWICE* the desired tuned >> frequency (because of the 2XLO mixers), and that input is limited to 8GHz, >> which means you can only >> use external LO usefully for center frequencies between 300Mhz and 4GHz. >> >> >> >> >> _______________________________________________ >> 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
