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_clock_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_src=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 _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
