[USRP-users] DOA with N310 or X310+TwinRX

Rob Kossler rkossler at nd.edu
Mon Jan 27 11:19:28 EST 2020


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 at 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-bounces at lists.ettus.com] *On Behalf
> Of *Sammy Welschen via USRP-users
> *Sent:* Monday, January 27, 2020 3:40 PM
> *To:* usrp-users at 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.Poehlmann at 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-bounces at lists.ettus.com] *On Behalf
> Of *Sammy Welschen via USRP-users
> *Sent:* Monday, January 27, 2020 2:19 PM
> *To:* usrp-users at 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 at 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.
>
>
>
>
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