Hi Rob, Robert, Sammy: Generally for this type of application we would recommend the X310+TwinRx. With the TwinRX, you'll be able to have repeatable phase offsets with a given gain, frequency, sample rate and temperature of a device/system. The N310 will have a 180 degree phase ambiguity due to the /2 LO architecture.
It is possible to share the LO across multiple motherboards for a X310/Twin setup, and with the NI branded X310+TwinRX setup (NI-2955) the LO's are provided out of the back panel. The chassis for currently shipping and Rev C, F, G X310's back plate has the holes for the LO cables, but the sticker needs to be removed. This application note covers the process: https://kb.ettus.com/Modifying_an_X310_Chassis_for_External_LO_Sharing You'll also need to provide a splitter and most likely an inline amplifier to overcome splitter losses. A splitter such as the ZFRSC-4-842+ will work. https://www.minicircuits.com/pdfs/ZFRSC-4-842+.pdf @Rob: With the current init process of the N310, yes it is required to first set the external LO to 5 GHz. With regards to the offsets you're seeing, I believe you should only see a possible phase difference of 180* within the two channels on the same DB. Are you issuing a tune request at the start of streaming? Regards, Nate Temple On Mon, Jan 27, 2020 at 8:20 AM Rob Kossler via USRP-users < usrp-users@lists.ettus.com> wrote: > Robert, Sammy, > I am presently running some tests which compare the X310/TwinRx and the > N310 with regard to channel-to-channel phase. In my setup, I have a signal > source that is split 8 ways (1:8 splitter) to feed the 4 channels of my > TwinRx and 4 channels of my N310. I have seen some strange behavior of the > N310 that perhaps Robert has experienced? Take a look: > > - For the TwinRx (for which I am a more experienced user with LO > sharing), I get consistent channel-to-channel phase difference among all > channels. This is true regardless of power cycles, re-starts of UHD, etc. > - For the N310 (for which I am a beginner when it comes to external LO > operation) > - it seems more complex to run in this mode (as compared to > TwinRx). In order to get it to work, I have had to disable startup QEC > calibration because it seems that the N310 initial cal occurs at 2500 > MHz > RF such that I would need to have my external LO at 5000 MHz for startup > (during the UHD deveice 'make') and then later switch my external LO to > the > desired RF*2. Is this true? > - when I run with either external LO or internal LO, I see > inconsistent channel-to-channel phase results even between the two > channels > of a given daughterboard that share the same LO. I do not understand > how > this is possible. My results over 16 captures (with some re-starts of > UHD, > device reboots, and switching between internal/external LO) show the > following channel-to-channel phase difference between channels 0 and 1 > which share the same LO: (values in degrees) -77, -19, -77, -19, -77, > -19, > -19, 39, -19, -19, -77, -19, -77, 39, -19, -19. Note that there are > only 3 > unique values and the delta happens to be 58 deg, but I don't know what > that implies... > > Rob > > > On Mon, Jan 27, 2020 at 9:57 AM Robert via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> With external LO its 300 MHz – 4 GHz, check footnote [3] from >> https://www.ettus.com/all-products/usrp-n310/. LO has to be supplied at >> twice the carrier freq. >> >> >> >> Currently we use 4 channels. You can find an example how to do the >> calibration here: https://github.com/EttusResearch/gr-doa >> >> gr-doa was written for TwinRX, but can be adapted. >> >> >> >> Phase noise behavior of N310 and N320/1 could be different, as N310 uses >> an RFIC and N32/1 use discrete components. This could be important if you >> want to operate in the small sample regime. >> >> >> >> >> >> *From:* USRP-users [mailto:usrp-users-boun...@lists.ettus.com] *On >> Behalf Of *Sammy Welschen via USRP-users >> *Sent:* Monday, January 27, 2020 3:40 PM >> *To:* usrp-users@lists.ettus.com >> *Subject:* Re: [USRP-users] DOA with N310 or X310+TwinRX >> >> >> >> Thank you for the information Robert! Isn't it 6 GHz? However, 4 GHz >> would also be sufficient for me. >> >> >> >> How many channels does your system have? I suppose you use some >> algorithm for phase calibration after power cycling? I plan to do the same, >> so the 180 deg ambiguity should be manageable. >> >> >> >> I looked at the N32x, however, they cost twice as much and I dont't plan >> on using 200 MHz of bandwidth. If I have an external LO signal I can feed >> it to the N310, so the only difference between N310 and N32x in this regard >> would be that I need to generate the LO externally when using the N310, >> right? >> >> >> >> <robert.poehlm...@dlr.de> schrieb am Mo., 27. Jan. 2020, 14:42: >> >> We use the N310 for DoA estimation, however: >> >> - you are limited to 4 GHz >> >> - after power-cycling you get a 180° ambiguity between the two >> radios (I do not know if this could also happen when you just change the LO >> frequency) >> >> >> >> If you want to have >4 channels, have a look at the new N320/N321. No >> experience with those, but apparently they can do LO distribution. >> >> >> >> Also take into account if maybe later in the project you want to be able >> to transmit, which you cannot do with TwinRX. >> >> >> >> Regards, >> >> Robert >> >> >> >> *From:* USRP-users [mailto:usrp-users-boun...@lists.ettus.com] *On >> Behalf Of *Sammy Welschen via USRP-users >> *Sent:* Monday, January 27, 2020 2:19 PM >> *To:* usrp-users@lists.ettus.com >> *Subject:* Re: [USRP-users] DOA with N310 or X310+TwinRX >> >> >> >> Thank you Marcus! So the N310 would be the way to go? I was unsure since >> the TwinRX is recommended for phase coherent applications. >> >> >> >> Marcus D. Leech via USRP-users <usrp-users@lists.ettus.com> schrieb am >> So., 26. Jan. 2020, 18:57: >> >> On 01/25/2020 11:43 AM, Sammy Welschen via USRP-users wrote: >> > Dear all, >> > >> > I am planning a system with 5-10 channels that is capable of DOA >> > estimation. >> > >> > Concerning the calibration of the resulting array, would there be a >> > difference between a system made up of N310 and one made up of X310 >> > with TwinRX boards? Would there be other important differences that >> > influence estimation performance? >> > >> > As I understand it, the TwinRX allows LO sharing between the boards in >> > a single X310, but this would not help me if I have two or three X310. >> > On the other hand, the N310s could be connected to a shared LO. >> > >> > Are the following thoughts correct? >> > >> > Suppose I turn on my system. Then I have to calibrate phase offsets >> > between channels in any case. Now I change the center frequency. If I >> > have N310s without shared LO, I have to recalibrate. Same for the >> > X310s, since LOs are shared only internally. If I have N310s with a >> > shared LO, I do not have to recalibrate. >> > >> > If I restart the system, I have to recalibrate in any case. >> > >> > The devices would by synchronized with PPS in any case and with the 10 >> > MHz reference if no external LO is used. >> > >> > What is the better choice for DOA estimation (N310 or X310 with TwinRX >> > or something different)? >> > >> > Thank you very much >> > >> > Sammy >> > >> > >> Sammy: >> >> Your characterization of the two scenarios is correct. >> >> There may be some folks on this list who have implemented DOA schemes, >> but likely few-to-none who have done it on both X310 and N310 >> and can comment on the differences they encountered. >> >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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