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

Sammy Welschen sammywelschen at gmail.com
Mon Jan 27 12:29:04 EST 2020


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 at 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 at 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 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.
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users at lists.ettus.com
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users at lists.ettus.com
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20200127/b2accbd5/attachment.html>


More information about the USRP-users mailing list