Hi Nate, thank you for the information. I'm still a bit unsure what repeatable phase offset means exactly. Suppose I have a system with 8 channels with X310+TwinRX and shared LO. Can I turn it off and come back the next day and still have the same phase offset between the channels that I had the day before?
Sammy Nate Temple via USRP-users <usrp-users@lists.ettus.com> schrieb am Mo., 27. Jan. 2020, 18:04: > 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 >> > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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