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

Nate Temple nate.temple at ettus.com
Tue Jan 28 15:03:09 EST 2020


Hi Sammy,

>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?

Yes. This assumes that you are running with the same frequency, gain,
sample rate and system temperature that your calibrations were made with.
Also unless you have phase stable cables, if you move your cables at all,
it can cause phase variation.


Regards,
Nate Temple

On Mon, Jan 27, 2020 at 9:29 AM Sammy Welschen <sammywelschen at gmail.com>
wrote:

> 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.
>>>>
>>>>
>>>>
>>>>
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