Hi Marcus,I have measured this with a spectrum analyzer simply by setting markers to the peak of the sinusoid (one marker per measured USRP) and then taking the delta.
Could it be that the USRP is ignoring the external reference when used alone? Remember, I am doing the test with one USRP at a time, as the test using multiple USRP simultaneously does not work.
Florian. On 06/12/2018 00:29, Marcus Müller wrote:
oh! That means 341 ppb frequency error, which *really* shouldn't be happening. I'd like to get some statistics of that error, how are you measuring it? Best regards, Marcus On Wed, 2018-12-05 at 12:55 +0100, Florian Kaltenberger wrote:Sorry typo. I did use a frequency of 3.51GHz.On 5 Dec 2018, at 12:54, Marcus Müller <marcus.muel...@ettus.com> wrote: Hi Florian, trying to get my head to understand the order of problems here: Could you try to use a higher frequency (say, --freq 2e9 instead of 3.5e6)? I'd thing 3.51 MHz is out of range for the N310, anyway? Best regards, Marcus On Wed, 2018-12-05 at 11:49 +0100, Florian Kaltenberger via USRP- users wrote:So I can confirm that there is a frequency offset between the two USRP N310s when using only an octoclock (10MHz + PPS) to synchronize. I have measured with the tx_waveforms program ./tx_waveforms --args "addr=192.168.x.2,time_src=external,clock_src=external,master_clo ck_r ate=122.88e6" --rate 122.88e6 --freq 3.51e6 --wave-type SINE -- wave- freq 10e6 --gain 100 on the first USRP N310 (x=10) and then on the other (x=20). There is an offset of 1200Hz between the peaks of the sinusoids between the two measurements. Using an external LO didn't change anything either. Unless I need to provide any other arguments in that case? I also tried to do a test where I use both USRPs simultaneously ./tx_waveforms --args "addr0=192.168.10.2,addr1=192.168.20.2,time_src=external,clock_sr c=ex ternal,master_clock_rate=122.88e6" --rate 122.88e6 --freq 3.51e6 -- wave-type SINE --wave-freq 10e6 --gain 100--channels "0,4" but unfortunately that does not work at all at my testbench (program hangs and no signal transmitted). My UHD version is 3.13.0.2 (UHD_3.13.0.HEAD-0-g0ddc19e5) Any help appreciated. Thanks! Florian.On 04/12/2018 21:29, Florian Kaltenberger via USRP-users wrote: Hi Marcus and Robin, thanks for your answers, this is helpful information. I should add, that I actually tried the synchronization with an octoclock (10MHz + PPS), but it did not give me the expected results, i.e., I saw some residual frequency offsets. But maybe I screwed up at some point. Let me do some more measurements and get back to you on this. Florian.On 04/12/2018 18:57, Marcus D. Leech via USRP-users wrote: On 12/04/2018 10:14 AM, Florian Kaltenberger via USRP-users wrote:Hi there, I just discovered that in addition to the external 10MHz reference in, the USRP N310 also has external local oscilator inputs, one for each daughterboard and each TX/RX. So does that mean that in order to synchronize multiple N310 in frequency, phase, and time, it is no longer sufficient to use an octoclock to provide a 10MHz reference and PPS? If so, at what frequency do you have to drive the external LOs and at what power? Florian.In addition to what Robin posted, I'll observe that the external LO port is an *additional feature* of this device. You should still be able to use the external 10MHz and 1PPS ports the same way you would with a B210 or E310, since the AD9371 front-end chip is similar to the AD9361 chip used in the B210 and E310. The thing about synchronizing multiple independent PLL synthesizers, though, compared to a strictly-shared-LO, is that the former will experience both phase ambiguities, and have a higher mutual phase-noise than the latter, which is why you might decide to choose the latter. _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com-- Follow us on Google+, LinkedIn, or Twitter! _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com-- Follow us on Google+, LinkedIn, or Twitter! _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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