Re: [Discuss-gnuradio] Phase Synchronization Across Channels in X310

[Zhan Yanjun]

Hi Marcus,

 

It works now! The DOA wrapper indeed ensured that the channels are phase-synchronous now. Thanks so much for your help!

 

Regards,

YJ

 

From: Marcus D. Leech <address@hidden>
Sent: Monday, 20 August 2018 08:38
To: Zhan Yanjun <address@hidden>; address@hidden
Subject: Re: [Discuss-gnuradio] Phase Synchronization Across Channels in X310

 

On 08/19/2018 08:11 PM, Zhan Yanjun wrote:

Hello Marcus,

 

Thanks for the reply. Yes, I do expect that there will be a constant phase offset that I will be able to compensate offline, however, the issue here is that everytime I start a new recording, the phase difference across the cards (and even between the 2 channels in the card) is always different. I would expect it to be the same everytime I record a signal.

 

Regards,

YJ

 

So, I would recommend looking at this app-note here, since gr-doa requires that all channels be phase-synchronous with zero phase-offset:

https://kb.ettus.com/Direction_Finding_with_the_USRP%E2%84%A2_X-Series_and_TwinRX%E2%84%A2

The gr-doa demonstrator code is here:

https://github.com/EttusResearch/gr-doa

From: Discuss-gnuradio <discuss-gnuradio-bounces+address@hidden> On Behalf Of Marcus D. Leech
Sent: Saturday, 18 August 2018 02:32
To: address@hidden
Subject: Re: [Discuss-gnuradio] Phase Synchronization Across Channels in X310

 

On 08/17/2018 05:37 AM, Zhan Yanjun wrote:

Hello everyone,

 

A while ago I came across an issue in running GNURadio with my version of UHD and I have followed instructions from the Ettus website https://kb.ettus.com/Building_and_Installing_the_USRP_Open-Source_Toolchain_(UHD_and_GNU_Radio)_on_Linux

 

Now the UHD version is UHD_3.11.0.HEAD-0-ga1b5c4ae, and the Gnuradio is version 3.7.13.4, and everything runs fine.

 

Everything was done on a fresh installation of Ubuntu 18.04.1 LTS.

 

Now, I want to do synchronous recording of all 4 channels on one X310 SDR chassis, but when I check the phase of the signal at each channel, they are not in phase.

 

Initially, I thought that it should have something to do with the internal LO, so I tried various combinations of the LO configuration:

1.     Internal, companion, companion, companion

2.     Internal, companion, external, external

3.     Internal, companion, external, companion

4.     all internal

But, it still does not work. I have connected the LO RF cables in a criss-cross fashion inside the chassis as well to pass the LO configuration to the neighbouring 2 channels.

 

Attached here is a snapshot of the GNURadio flowchart I designed for that purpose.

 

I also tried to install the latest UHD version in my computer, but it is unable to work with FPGA image (non-release version). Because the X310 are not mine, I cannot update FPGA image.

 

Have you all come across this issue before? Please share your views on this, any help is much appreciated! I have tried installing and reinstalling the programs a few times, but the conclusion is still the same, and the phases across the channels do not match.

 

Thanks and regards,

YJ

 

Don't forget that the LO link cables are of non-zero length electrically, so there will be some phase offset between the two cards that you'll need
  to compensate for.