Hi Marcus,
yesterday I got the deviations of 0.3 rad by fluke. Even after receiving using two RX2 ports the phase difference is deviating to large values like 2 rad. I tried disabling I/Q corrections by passing 0 to the property field but that too didn't work. I think I really now need to use splitter to find out so need to wait. If meanwhile I can try something else then please let me know. Regards, Koyel ________________________________ From: USRP-users <usrp-users-boun...@lists.ettus.com> on behalf of Koyel Das (Vehere) via USRP-users <usrp-users@lists.ettus.com> Sent: Monday, September 17, 2018 9:23:33 PM To: Marcus D. Leech Cc: 'USRP-users@lists.ettus.com' Subject: Re: [USRP-users] Sampler clock common or not? Hi Marcus, My colleague suggested not to use TX/RX port and I did that. I just tested two sets of data of stationary wifi with both antennas this time connected to RX2 port as he suggested and then the phase difference deviation goes maximum to 0.3 rad. I will carry out experiments with more data sets to see if I always get same types of deviation. Regards, Koyel ________________________________ From: Marcus D. Leech <mle...@ripnet.com> Sent: Monday, September 17, 2018 9:16:13 PM To: Koyel Das (Vehere) Cc: 'USRP-users@lists.ettus.com' Subject: Re: [USRP-users] Sampler clock common or not? On 09/17/2018 06:31 AM, Koyel Das (Vehere) wrote: Hi Marcus, I am looking at the following link https://files.ettus.com/schematics/x300/x3xx.pdf and as you said same clock is being used by both the boards. NI has asked for some time to find it out. Regards, Koyel You might try disabling I/Q corrections in your flow-graph, and see if that helps. ________________________________ From: Koyel Das (Vehere) Sent: Monday, September 17, 2018 12:57:29 PM To: Marcus D. Leech; Koyel Das (Vehere) Subject: Re: [USRP-users] Sampler clock common or not? Hi Marcus, I spoke with NI and they are saying that in USRP 2954 R there are two LOs for two daughter boards which are not locked to any master oscillator. They are not phase locked but we can provide a reference clock if we want them to run coherently. He said in 2955 R LO sharing is there so we can share single LO for 4 daughter boards. Regards, Koyel ________________________________ From: USRP-users <usrp-users-boun...@lists.ettus.com><mailto:usrp-users-boun...@lists.ettus.com> on behalf of Koyel Das (Vehere) via USRP-users <usrp-users@lists.ettus.com><mailto:usrp-users@lists.ettus.com> Sent: Monday, September 17, 2018 12:12:32 PM To: Marcus D. Leech; 'USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com>' Subject: Re: [USRP-users] Sampler clock common or not? Hi, I don't have a splitter currently. So to use it I need to wait until it arrives. I din't find uhd_fft in gnuradio. I am using gnuradio-companion. However, I see similar issues faced by some other people: https://lists.gnu.org/archive/html/discuss-gnuradio/2008-04/msg00029.html Regards, Koyel RE: [Discuss-gnuradio] Compare Phase block<https://lists.gnu.org/archive/html/discuss-gnuradio/2008-04/msg00029.html> lists.gnu.org My VOR receiver is almost there, but not quite... My code is below. I've demodulated the first 30 Hz signal from AM, and the second from the FM subcarrier. ________________________________ From: Marcus D. Leech <mle...@ripnet.com><mailto:mle...@ripnet.com> Sent: Sunday, September 16, 2018 9:28:55 AM To: Koyel Das (Vehere); 'USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com>' Subject: Re: [USRP-users] Sampler clock common or not? On 09/15/2018 11:54 PM, Koyel Das (Vehere) wrote: I just forwarded in another thread the processing I am doing. Have you received it? Regards, Koyel Yes, but I'd rather not have to analyse your MATLAB code in detail. You can use the --phase-relations option on the uhd_fft utility for doing two-channel phase-coherence measurements in real-time. Unless something is horribly broken, two UBX cards on the same underlying USRP platform WILL operate with mutual coherence, with some initial phase-offset, just due to the way synthesizers work. But that phase offset will carry-forward in time, with only very minor phase noise perturbations just due to the physics of semiconductors, etc. ________________________________ From: Marcus D. Leech <mle...@ripnet.com><mailto:mle...@ripnet.com> Sent: Sunday, September 16, 2018 9:05:29 AM To: Koyel Das (Vehere); 'USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com>' Subject: Re: [USRP-users] Sampler clock common or not? On 09/15/2018 11:32 PM, Koyel Das (Vehere) wrote: I don’t have access to the flowgraph currently but it’s the same flowgraph I sent earlier in my other previous email for 2955 R. I have UHD with two channels, each channel connected to a file sink. One channel is set to TX/RX, another to RX2. I am sampling at 1 msps. I am capturing data from two channels, storing in file and then reading them in matlab and cross correlating them to get phase difference but the phase difference for any particular frequency bin is showing deviations with time. Deviations are huge sometimes +-pi. Regards, Koyel I would say that you're doing something wrong in the post-processing. I routinely use USRPs of all types for interferometry in radio astronomy, where the long term phase noise has to be very low, or your data is rubbish. ________________________________ From: Marcus D. Leech <mle...@ripnet.com><mailto:mle...@ripnet.com> Sent: Sunday, September 16, 2018 8:48:26 AM To: Koyel Das (Vehere); 'USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com>' Subject: Re: [USRP-users] Sampler clock common or not? On 09/15/2018 10:38 PM, Koyel Das (Vehere) wrote: Hi, Thanks for the information. Do I have to set any property in the gnu radio uhd to phase lock the two oscillators to on board clock or they are by default locked to it? Nothing special to do. It happens automatically. Can the external reference be gps? What settings need to be done in UHD to sync the two oscillators to gps? There's a good knowledge-base article on this and many other topics here: https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices Actually I am receiving a stationary signal using two ports TX/RX and RX2 but I am not getting a constant phase difference with time. It can happen if two oscillators are not synced . The starting phase between the two sides will not be anything in particular. But after that, they'll have a constant phase difference. What are you using to measure the phase different between the two channels. How is the signal delivered to the two channels? Can you share your Gnu Radio flow-graph? Please help. ________________________________ From: USRP-users <usrp-users-boun...@lists.ettus.com><mailto:usrp-users-boun...@lists.ettus.com> on behalf of Marcus D. Leech via USRP-users <usrp-users@lists.ettus.com><mailto:usrp-users@lists.ettus.com> Sent: Sunday, September 16, 2018 5:10:23 AM To: usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com> Subject: Re: [USRP-users] Sampler clock common or not? On 09/15/2018 01:35 AM, Koyel Das (Vehere) via USRP-users wrote: Hi, I am using USRP 2954R. I have connected one antenna to RX2 of RF0 and another antenna to TX/RX of RF1. Both are used for receiving. Can someone tell me if RX2 of RF0 and TX/RX of RF1 are phase locked that is the signal received by the two have a constant phase difference with time or not? Are the two LOs controlled by a common master oscillator or two LOs run Independently? Regards, Koyel Both synthesizers are phase-locked to either the on-board clock, or an external reference clock, if you're using an external reference. So, they'll have no relative phase-drift with respect to one another (except for thermal effects, but those have a very small magnitude).
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