Ok. False alarm. I forgot about the dboard clock needing set to 20MHz for RF freq below 1 GHz. When I made this change, now I get consistent Rx-Tx phase for the first mode where both Tx and Rx start/stop at each test. Rob
On Thu, Mar 19, 2020 at 6:10 PM Rob Kossler <rkoss...@nd.edu> wrote: > Ok. I modified my code to be more like yours... > > - toggling dsp freq rather than LO freq > - LO at 900 MHz > - external connections Tx0 => Splitter_1x2 => both Rx0 and Rx1 > - Previously, I was starting / stopping both Rx & Tx in between each > test. Now, I added a mode where the Tx is on continuously, and the Rx > starts & stops for each test after the dsp freq change > > The results are the following: > > - In the first mode where both Tx and Rx start/stop at each test, I > get consistent group delay (as measured by the correlation peak index) for > both Rx-Rx and Rx-Tx. But for phase, the Rx-Rx phase is consistent, but > the Rx-Tx phase seems random > - In the second mode where Tx is on continuously and I start/stop Rx > after each dsp freq change, the group delay is constant for Rx-Rx but > random for Rx-Tx. The phase results are constant for Rx-Rx but random for > Rx-Tx. > > Regarding the 2nd mode, this makes sense to me. But, for the 1st mode, I > don't understand why the Rx-Tx phase seems random. Still thinking about > it.... > Rob > > > On Thu, Mar 19, 2020 at 4:35 PM Rob Kossler <rkoss...@nd.edu> wrote: > >> Lukas, >> Just before receiving your email, I ran the following with my custom c++ >> & matlab software using X310/UBX-160 with the connections I described. The >> following shows the output which is very consistent. I used a 100 tone >> multi-tone waveform spread over 4 MHz bandwidth (using 5 MS/s sample rate >> on Tx and Rx). Note the consistency of results as I toggled between 2 >> frequencies: 2450 and 2460 MHz. >> >> My method was the following: >> >> - Tx waveform was 500 points long >> - Rx capture was 5000 points long >> - Compute cross-correlation (using Matlab xcorr) as follows: >> xcorr(rx0, conj(tx)) AND xcorr(rx0,conj(rx1)) >> - Find the correlation peak (which was very pronounced) which shows >> the sample delay between the two signals. Extract the phase at the peak >> >> Oops, I just realized that I used a constant DSP freq (10 MHz) and I >> changed the LO freq in my test. I will try again with moving the DSP freq >> instead. >> Rob >> >> Test 1: freq = 2450.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -121.8 >> Rx0/Rx1 xcorr peak at index 115 with phase -95.7 >> Test 2: freq = 2460.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -58.7 >> Rx0/Rx1 xcorr peak at index 115 with phase 13.1 >> Test 3: freq = 2450.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -121.7 >> Rx0/Rx1 xcorr peak at index 115 with phase -95.8 >> Test 4: freq = 2460.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -58.6 >> Rx0/Rx1 xcorr peak at index 115 with phase 13.0 >> Test 5: freq = 2450.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -121.7 >> Rx0/Rx1 xcorr peak at index 115 with phase -95.8 >> Test 6: freq = 2460.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -58.8 >> Rx0/Rx1 xcorr peak at index 115 with phase 12.7 >> Test 7: freq = 2450.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -121.8 >> Rx0/Rx1 xcorr peak at index 115 with phase -95.9 >> Test 8: freq = 2460.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -58.7 >> Rx0/Rx1 xcorr peak at index 115 with phase 12.9 >> Test 9: freq = 2450.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -121.8 >> Rx0/Rx1 xcorr peak at index 115 with phase -95.8 >> Test 10: freq = 2460.0 MHz >> Rx0/Tx0 xcorr peak at index 108 with phase -58.7 >> Rx0/Rx1 xcorr peak at index 115 with phase 12.9 >> >> >> >> >> On Thu, Mar 19, 2020 at 4:21 PM Lukas Haase <lukasha...@gmx.at> wrote: >> >>> Hi Rob, >>> >>> Yes, I confirm your conclusion. >>> >>> >>> - I calculate the relative phase by dividing the outputs of both >>> receivers. To understand better, note that I have an additional "IF >>> stage" >>> in my own signal flow such that I exclude DC offset correction etc. the >>> USRP may perform. This is the block diagram of the transmitter part: >>> https://snipboard.io/YFgIKs.jpg . I send "exp(1j*1MHz*t) . This >>> shows the receiver part: https://snipboard.io/i9jLJg.jpg . I >>> multiply the received signal with exp(-1j*1MHz*t) and filter them. Then I >>> divide both streams and take the phase part. I take a moving average (for >>> flucatuations), add pi and display the number. >>> - https://snipboard.io/YFgIKs.jpg https://snipboard.io/YFgIKs.jpg >>> https://snipboard.io/YFgIKs.jpg That's so nice, thank you!! My code >>> is here: http://paste.ubuntu.com/p/MbCJfPGzYW/ . I'm not sure if you >>> have gnuradio(and QT) installed but if yes, simply "python2 >>> switch_on_click.py" should do. Let me quickly elaborate how it works: >>> - Class "switch_on_click" implements a normal gnuradio flow with >>> USRP transmitter and receiver. >>> - It also uses a custom module together with buttons and a probe >>> block to call functions upon clicking on a button >>> - The callback functions are defined in class "blk" >>> - The most important is "def button_rtx_handler" on line 106 >>> which is executed when user clicks on button "Switch RTX (together)" >>> - Again, thank you for trying this out!! If it works, would you mind >>> sharing this code then? I may be able to check then where it breaks on my >>> system >>> - I use 900 MHz as default center frequency (and "rf_freq"). When >>> clicking, I jump between dsp_freq=0 and dsp_freq=500e3. As to my >>> waveform, >>> you can infer from my screenshots and code above: I am transmitting and >>> receiving a 1MHz waveform (which acts as an additional "IF stage"). The >>> received signal is then downconcerted from 1MHz to DC. I use 5 MSsps >>> sampling rate. >>> >>> >>> Again, thank you SO much. >>> >>> Best, >>> Lukas >>> >>> >>> *Gesendet:* Donnerstag, 19. März 2020 um 10:43 Uhr >>> *Von:* "Rob Kossler" <rkoss...@nd.edu> >>> *An:* "Lukas Haase" <lukasha...@gmx.at> >>> *Cc:* "USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> >>> *Betreff:* Re: [USRP-users] USRP X310 ignored DSP retuning on TX when >>> using a timed command >>> Hi Lukas, >>> So, the conclusion is that your Rx0-to-Rx1 relative phase is nearly >>> constant such that it seems that both Rx0/Rx1 are phase coherent and >>> Tx0/Tx1 are phase coherent. But, phase from Tx-to-Rx is random. Please >>> correct me if that is wrong. >>> >>> I have a few comments: >>> >>> - How do you measure/calculate the relative phase? >>> - Can you send me the full Python code to look at? As I mentioned >>> previously, I am not too good at gnuradio/Python, but I might be able to >>> spot something. >>> - As to your question, I always use synchronous measurements. And, >>> I'm confident that my Rx-to-Rx phase is coherent. But, I haven't really >>> looked at Tx-to-Rx in a while so I will do so later today. Here are the >>> steps I plan to take: >>> 1. Connect Tx0 to Rx1. Note that there is a pretty strong >>> leakage signal from Tx0 to Rx0 so I don't really need to provide a >>> physical >>> connection in order to get a signal on Rx0. The signal attenuation >>> in this >>> leakage path is approx 40 dB so it is not too much different than the >>> signal level I will receive on Rx1 if I use an external 30 dB >>> attenuator. >>> 2. Set Rx and Tx frequency to freq 1 >>> 3. Measure and note the relative phase for Rx0/Tx0 and Rx1/Tx0 >>> for freq 1 >>> 4. Set Rx and Tx frequency to freq 2 >>> 5. Measure and note the relative phase for Rx0/Tx0 and Rx1/Tx0 >>> for freq 2 >>> 6. Repeat steps 2-5 a few times to ensure that the measurements >>> are repeatable >>> - Questions: what should I use for freq 1 and freq 2? What waveform >>> are you transmitting? What sample rates for Tx and Rx? >>> >>> Rob >>> >>> >>> >>> On Wed, Mar 18, 2020 at 7:47 PM Lukas Haase via USRP-users < >>> usrp-users@lists.ettus.com> wrote: >>> >>>> Hi Rob, >>>> >>>> I think the issue is really having two usrp_multi devices with timed >>>> commands and same timestmap or similar. From your tests below: >>>> >>>> 1.) I can *confirm *that the relative phase between two RX in your >>>> suggested test is always the same! In fact, it is always 4.56 rad, even >>>> across restarts and for different frequencies! That somewhat makes sense >>>> because the phase offset is now only dependent on the difference between >>>> the two channels (fixed) and cable lengths from the splitter (fixed). I >>>> verified by removing the timed command on usrp source, the phase offset >>>> becomes random after each retune. Of course, this is independent of TX >>>> tuning (timed vs. not). For reference, this is the code used: >>>> >>>> tune_req_rx = uhd.tune_request() >>>> tune_req_rx.rf_freq_policy = uhd.tune_request.POLICY_NONE >>>> tune_req_rx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >>>> tune_req_rx.dsp_freq = -dsp_freq >>>> tune_req_tx = uhd.tune_request() >>>> tune_req_tx.rf_freq_policy = uhd.tune_request.POLICY_NONE >>>> tune_req_tx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >>>> tune_req_tx.dsp_freq = dsp_freq >>>> >>>> now = usrp_sink.get_time_now() >>>> when = now + uhd.time_spec(1.0) >>>> >>>> usrp_sink.set_command_time(when) >>>> usrp_source.set_command_time(when) >>>> res1 = usrp_sink.set_center_freq(tune_req_tx) # TX >>>> res2 = usrp_source.set_center_freq(tune_req_rx, 0) #RX1 >>>> res3 = usrp_source.set_center_freq(tune_req_rx, 1) #RX2 >>>> usrp_sink.clear_command_time() >>>> usrp_source.clear_command_time() >>>> >>>> 2.) I also tried your second suggestion. Before reading on, you wanna >>>> guess what the outcome is? >>>> I connected "TX/RX" to "RX2" on UBX #1 (TX1 --> RX1) and "TX/RX" to >>>> "RX2" on UBX #2 (TX2 --> RX2). In absence of a second 30dB attenuator I >>>> used two antennas closely spaced together. For reference, my code looks now >>>> like: >>>> >>>> tune_req_rx = uhd.tune_request() >>>> tune_req_rx.rf_freq_policy = uhd.tune_request.POLICY_NONE >>>> tune_req_rx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >>>> tune_req_rx.dsp_freq = -dsp_freq >>>> tune_req_tx = uhd.tune_request() >>>> tune_req_tx.rf_freq_policy = uhd.tune_request.POLICY_NONE >>>> tune_req_tx.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL >>>> tune_req_tx.dsp_freq = dsp_freq >>>> >>>> now = usrp_sink.get_time_now() >>>> when = now + uhd.time_spec(1.0) >>>> >>>> usrp_sink.set_command_time(when) >>>> usrp_source.set_command_time(when) >>>> res1 = usrp_sink.set_center_freq(tune_req_tx, 0) # TX1 >>>> res2 = usrp_sink.set_center_freq(tune_req_tx, 1) # TX2 >>>> res3 = usrp_source.set_center_freq(tune_req_rx, 0) # RX1 >>>> res4 = usrp_source.set_center_freq(tune_req_rx, 1) # RX2 >>>> usrp_sink.clear_command_time() >>>> usrp_source.clear_command_time() >>>> >>>> I again look at the *relative phase* of RX1 and RX2 (obtained by >>>> dividing the two) and guess what: Also now the relative phase stays >>>> constant! (This time it actually slightly varies from 3.0 rad to 3.7 rad >>>> between two different frequencies). >>>> What does that mean? I think it means that TX must be tuned coherently >>>> and RX must be tuned coherently, i.e., timed commands generally work for >>>> multiple TX's and multiple RX's *individually*. Do I get that right? >>>> >>>> What doesn't seem to work is RX+TX *together*. >>>> >>>> I am very desperately asking if you had coherent TX+RX setup working at >>>> any point or know somebody who did. It would be so much worth to know if >>>> this is something that never worked to begin with or if I'm just doing >>>> something wrong. On the other hand I don't want to believe being the only >>>> person on the planet having tried TX+RX phase coherent operation :-/ >>>> >>>> Any other further suggestions on how to continue debugging with the >>>> above in mind would be helpful too. >>>> >>>> In my opinion there are two options left: >>>> 1.) There is still a nondeterministic delay between the TX and RX timed >>>> commands (to my understanding, even a constant delay would result in >>>> coherent phase) >>>> 2.) While the phase accumulators in RX are set to the same values (and >>>> in TX as well), they may be set to a different, random value. >>>> >>>> However, I don't really know how to test these. >>>> >>>> Thanks, >>>> Lukas >>>> >>>> >>>> *Gesendet:* Freitag, 13. März 2020 um 12:27 Uhr >>>> *Von:* "Rob Kossler" <rkoss...@nd.edu> >>>> *An:* "Lukas Haase" <lukasha...@gmx.at> >>>> *Cc:* "Marcus D Leech" <patchvonbr...@gmail.com>, " >>>> USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> >>>> *Betreff:* Re: [USRP-users] USRP X310 ignored DSP retuning on TX when >>>> using a timed command >>>> Ok, great. I am trying to think of ways to now add the phase >>>> measurement. Ideas... >>>> >>>> - In order to get consistent phase, you would need to tune Rx and >>>> Tx DSP at the same time (rather than below where you are only tuning >>>> one of >>>> them). So, assuming that this will not produce consistent phase >>>> results, >>>> then maybe try the following idea... >>>> - If you want to check just Rx DSP tuning (with fixed Tx DSP >>>> tuning), you could try a 2 channel Rx measurement where the Tx is split >>>> externally with 1:2 splitter in order to drive both Rx0 and Rx1. Then, >>>> measure the relative phase Rx0/Rx1 and then tune back and forth between >>>> two >>>> Rx DSP freqs to see if the relative phase on Rx remains constant. If >>>> so, >>>> this would give you good confidence that Rx DSP tuning is indeed >>>> happening >>>> synchronously >>>> - Assuming that the Rx IS synchronous in the step above (perhaps a >>>> bad assumption, but here goes), you could then check TX DSP tuning (with >>>> fixed Rx DSP tuning) by using two Tx and two Rx channels with Tx0 >>>> connected >>>> to Rx0 and Tx1 connected to Rx1. At this point we are confident that Rx >>>> DSP tuning is synchronous so any synchronous misbehavior would imply a >>>> Tx >>>> sync problem. >>>> >>>> Sorry I can't think of better ideas. >>>> Rob >>>> >>>> On Fri, Mar 13, 2020 at 12:12 PM Lukas Haase <lukasha...@gmx.at> wrote: >>>> >>>>> Hi Rob, >>>>> >>>>> 1.) yes, works(*) >>>>> 2.) yes, works(*) >>>>> >>>>> (*): qualitatively. I set the timed command to "get_current_time() + >>>>> uhd.time_spec(2.0)" and I see the chance 2 seconds after my click on the >>>>> screen. I cannot (do not know how) check if it actually happens at >>>>> sample-precicse location. >>>>> >>>>> Great, any ideas to simplify the setup would nice. I just don't know >>>>> how I could continue to debugging the phase. >>>>> >>>>> Best, >>>>> Luke >>>>> >>>>> >>>>> Gesendet: Freitag, 13. März 2020 um 11:08 Uhr >>>>> Von: "Rob Kossler" <rkoss...@nd.edu> >>>>> An: "Lukas Haase" <lukasha...@gmx.at> >>>>> Cc: "Marcus D Leech" <patchvonbr...@gmail.com>, " >>>>> USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com> >>>>> Betreff: Re: [USRP-users] USRP X310 ignored DSP retuning on TX when >>>>> using a timed command >>>>> >>>>> Thanks Lukas, >>>>> I wanted to confirm that you did not have an older version of FPGA >>>>> firmware because there was a DDC/DUC bug fix[ >>>>> https://github.com/EttusResearch/fpga/commit/0b2364653405612a6d5dfaa0e69b1c6798771e6d] >>>>> related to phase. However, the version you provided with uhd_usrp_probe >>>>> confirms that you have the bug fix included. So, this is not the problem. >>>>> >>>>> From what you said, I assume that you can successfully do the >>>>> following: >>>>> 1) with Rx tuning fixed (no re-tuning at all), tune Tx DSP only (do >>>>> not change TX RF) and you can see the frequency change at the specified >>>>> command time (i.e., if you specify the command time 1 sec in the future, >>>>> the change does not occur until 1 sec in the future). >>>>> 2) opposite of #1: with Tx tuning fixed, tune Rx DSP only and you can >>>>> see the frequency change at the specified command time. >>>>> >>>>> I am trying to simplify the issue by removing RF tuning completely and >>>>> by tuning only 1 of Rx/Tx at a time. Perhaps this will help lead to the >>>>> answer. >>>>> Rob >>>>> >>>>> >>>>> >>>>> On Fri, Mar 13, 2020 at 10:53 AM Lukas Haase <lukasha...@gmx.at >>>>> [mailto:lukasha...@gmx.at]> wrote:Hi again Rob, >>>>> >>>>> Yes, I confirm: >>>>> >>>>> 1.) Finally I get the commands to execute at the same time (TX and RX >>>>> individually and both at the same time) >>>>> 2.) Yes, the phase is random after each retune, even when I retune >>>>> back to the same frequency >>>>> 3.) (2) is only true if it includes *DSP* retuning. With naalog >>>>> retuning (+integer-N retuning) I get phase coherence, as expected. >>>>> >>>>> I actually expected the PLL retuning much more challenging than the >>>>> DSP retuning but for some reason it seems to be the opposite... >>>>> >>>>> Thanks, >>>>> Lukas >>>>> >>>>> >>>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list >>>> USRP-users@lists.ettus.com >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >>>
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