Is it possible to run two LO cables out of channel 4 and into channel 5 such that channel 5 & 6 should be configured as "external" rather than as "internal/companion"? I realize that there is no external RF connector to support the cables passing from USRP 1 to USRP 2, so you would have to figure out how you would want to do that.
Rob On Thu, Sep 13, 2018 at 10:48 PM Marcus D. Leech via USRP-users < [email protected]> wrote: > On 09/13/2018 10:12 PM, Jack Yang wrote: > > Hi Marcus, > > Thanks for the prompt reply. I have two questions. First, I remember I can > align phase across multiple USRPs when using UBX-160 daughterboards (i.e 4 > USRPs equipped with 8 UBX-160 for 8 phase-array receivers.). Just to double > confirm that I cannot use the UBX-160 time configuration approach to align > phase for TwinRx across two USRPs, right? Since TwinRxs use superheterodyne > structure, the time setting configuration for phase alignment (which work > for UBX-160) will not work for the TwinRx due to the second stage > down-conversion having it's own LO and this LO is not able to access from > the other USRP. Is my understanding correct? > > That is correct, as far as I understand the architecture of the TwinRX. > > > My second questions is that do you know any approach which can have self > calibration for each run? If I use two port RF splitter to connect Rx4 in > the first USRP and Rx5 in the second USRP for the same antenna as input, > ideally I can use the Rx4 & Rx5 phase difference to compensate other three > receivers in the second USRP. Then, I can still set up a 7 receivers for > coherent receivers, right? > > The usual approach is "measure and correct". This works well if you have: > > (A) A calibration source you can turn on that is visible to all inputs and > of equal phase delay > > or > > (B) You have some continuous, but distant, signal source that is "seen" by > all your receivers > > or > > (C) Other schemes that achieve the same thing > > The key is that you have to measure the phase delays and compensate. > > > > Really thanks for your time to answer my questions! > > All Best, > Jack > > > > On Thu, Sep 13, 2018 at 6:20 PM Marcus D. Leech via USRP-users < > [email protected]> wrote: > >> On 09/13/2018 08:52 PM, Jack Yang via USRP-users wrote: >> > Hi, >> > >> > I am trying to set up a 8 channels coherent receiver where I am using >> > two X310 and each X310 is equipped with two TwinRx. However, the phase >> > alignment across two USRP are always failed. The two X310 are using >> > the OctoClock-G to have 1M PPS and 10MHz clock. Then, I am using a >> > individual transmitter which can generate single tone with RF splitter >> > to connect to the 8 channels via RF coaxial cable. My GNURadio >> > configuration is shown as below the link ( >> > https://www.dropbox.com/s/du15rakg1nacmql/DualX310_8Rec_v1.py?dl=0 ). >> > Alternatively, one can also see the below summary configuration. I >> > can have constant phase difference within the same USRP when I power >> > on and off for different trials, while the phase difference across two >> > USRP are always varying for each trial (i.e The phase difference >> > between Ch4 in first USRP and Ch5 in second USRP is not constant among >> > different runs). The below links refer to the results for two >> > different trials. In first trials, all the phase difference is shifted >> > based on itself mean value (First run, >> > https://www.dropbox.com/s/z8so39bejzdofi8/Run1.png?dl=0 ). Then, using >> > the first-run average phase difference to compensate the phase >> > difference in the second run (Second run, >> > https://www.dropbox.com/s/xhkmp6cuxzwylvx/Run2.png?dl=0 ). As the >> > result shown in the second run, the phase difference across Rx5 and >> > Rx3 has been shifted to -214 degrees while all the other phase >> > difference within itself USRP are still the same as the previous >> > measurement. Could someone let me know how I can configure two USRP >> > X310 with TwinRx for the coherent receivers? >> > >> > Many thanks for the help! >> > >> > All Best, >> > Jack >> > >> So in the first USRP, your TwinRx is configured to share the LO from the >> first channel to the other 3 channels. The only phase-offset compensation >> you'll need to do is fixed, and is dominated just by the length of >> the cables within the enclosure that are used to share LOs. >> >> However, in the second USRP, THAT LO is independent from the one on the >> first X310, even though it uses a common phase reference >> (the 10MHz shared between the two). What this means is that the two >> USRPs won't drift relative to one another, but there will be >> some unknown phase offset between them, due to the way that RF >> synthesizers work--you have two synthesizers (one in the first USRP >> on one of the TwinRX cards), and the other in the second. They won't >> agree on startup phase, except "by accident". You'll have to resolve >> this using a calibration procedure. There's really no way around >> that with this type of architecture. >> >> >> >> _______________________________________________ >> USRP-users mailing list >> [email protected] >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > > _______________________________________________ > USRP-users mailing list > [email protected] > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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