Ah, excellent. I believe you are correct. If I up the frequency, the period reduces, so I can see more of the imposed modulation. So, forgive my ignorance, but how does one correct this? thanks very much! Steven Knudsen, Ph.D., P.Eng. www. techconficio.ca <http://techconficio.ca/> www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen> Von einem gewissen Punkt an gibt es keine Rückkehr mehr. Dieser Punkt ist zu erreichen. - Franz Kafka > On Sep 15, 2016, at 10:57, Torell, Kent <Kent.Torell@gd-ms.com <mailto:Kent.Torell@gd-ms.com>> wrote: > > It’s a low frequency carrier error, so you are seeing the bpsk roll into the other quadrature, then invert data. > > From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com <mailto:usrp-users-bounces@lists.ettus.com>] On Behalf Of Steven Knudsen via USRP-users > Sent: Thursday, September 15, 2016 9:50 AM > To: USRP-users > Cc: Knud > Subject: [USRP-users] B200mini and low-freq modulation of tx'd signal > > Hi, > > I have a TDMA flowgraph that defines packets using tx_time and tx_sob + tx_eob. Packets are sent to a B200mini every 10 ms (which is not important). Below I have the packet format from GRC followed by 3 oscilloscope captures that show the effect I’m seeing. > > The B200mini is connected to an Octoclock 1 PPS reference. > > The modulation is BPSK, 2x oversampled, RRC. > > Image 1 - the GRC waveform that is input to the USRP sink > Image 2 - this time the transmitted signal looks pretty good. Note the leading zeros so that the transmit power rises to full before samples are applied. > Image 3 - it appears that some form of slow modulation has been applied > Image 4 - same again, but obviously at a different offset > > (oops, forgot to turn off stupid network config menu in scope caps) > > I am a bit stumped. A “theory” is that maybe I’m seeing a window of some kind being convolved with the signal. > > <image001.png> > > <image002.jpg> > > <image003.jpg> > > <image004.jpg> > > > Steven Knudsen, Ph.D., P.Eng. > www. techconficio.ca <http://techconficio.ca/> > www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen> > > Der entscheidende Augenblick der menschlichen Entwicklung ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, welche alles Frühere für nichtig erklären, im Recht, denn es ist noch nichts geschehen. - Franz Kafka >

You will need to recover the carrier frequency at the receiver. For small errors, you can simply use a PLL for this. Cheers, Martin On 09/15/2016 10:54 AM, Steven Knudsen via USRP-users wrote: > Ah, excellent. I believe you are correct. If I up the frequency, the > period reduces, so I can see more of the imposed modulation. > > So, forgive my ignorance, but how does one correct this? > > thanks very much! > > > Steven Knudsen, Ph.D., P.Eng. > www. techconficio.ca <http://techconficio.ca> > www.linkedin.com/in/knudstevenknudsen > <http://www.linkedin.com/in/knudstevenknudsen> > > /Von einem gewissen Punkt an gibt es keine Rückkehr mehr. Dieser Punkt > ist zu erreichen. - Franz Kafka/ > >> On Sep 15, 2016, at 10:57, Torell, Kent <Kent.Torell@gd-ms.com >> <mailto:Kent.Torell@gd-ms.com>> wrote: >> >> It’s a low frequency carrier error, so you are seeing the bpsk roll >> into the other quadrature, then invert data. >> >> *From:* USRP-users [mailto:usrp-users-bounces@lists.ettus.com] *On >> Behalf Of *Steven Knudsen via USRP-users >> *Sent:* Thursday, September 15, 2016 9:50 AM >> *To:* USRP-users >> *Cc:* Knud >> *Subject:* [USRP-users] B200mini and low-freq modulation of tx'd signal >> >> Hi, >> >> I have a TDMA flowgraph that defines packets using tx_time and tx_sob >> + tx_eob. Packets are sent to a B200mini every 10 ms (which is not >> important). Below I have the packet format from GRC followed by 3 >> oscilloscope captures that show the effect I’m seeing. >> >> The B200mini is connected to an Octoclock 1 PPS reference. >> >> The modulation is BPSK, 2x oversampled, RRC. >> >> Image 1 - the GRC waveform that is input to the USRP sink >> Image 2 - this time the transmitted signal looks pretty good. Note the >> leading zeros so that the transmit power rises to full before samples >> are applied. >> Image 3 - it appears that some form of slow modulation has been applied >> Image 4 - same again, but obviously at a different offset >> >> (oops, forgot to turn off stupid network config menu in scope caps) >> >> I am a bit stumped. A “theory” is that maybe I’m seeing a window of >> some kind being convolved with the signal. >> >> <image001.png> >> >> <image002.jpg> >> >> <image003.jpg> >> >> <image004.jpg> >> >> >> Steven Knudsen, Ph.D., P.Eng. >> www. techconficio.ca <http://techconficio.ca/> >> www.linkedin.com/in/knudstevenknudsen >> <http://www.linkedin.com/in/knudstevenknudsen> >> >> /Der entscheidende Augenblick der menschlichen Entwicklung >> ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, >> welche alles Frühere für nichtig erklären, im Recht, denn es ist >> noch nichts geschehen. - Franz Kafka/ >> > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >

Thanks for the response. I was having an off day, seeing issues that I should have understood. The Correlation Estimator Block works fine for my purposes, giving a phase_est that I use to correct the frequency offset. What I’m finding (and this should not be part of this list I know), is the usual problem with a multi-radio, packet-based system. Many GNU Radio blocks are meant to deal with non-idealities for stream-based transmissions from a single transmitter. So, for example, the Polyphase Clock Sync tracking breaks down in this circumstance. I should know better and am busy adding algorithms that use my packet preamble to do various estimations and corrections. Sorry to waste the “list’s” time… steven Steven Knudsen, Ph.D., P.Eng. www. techconficio.ca www.linkedin.com/in/knudstevenknudsen All the wires are cut, my friends Live beyond the severed ends. Louis MacNeice > On Sep 21, 2016, at 10:55, Martin Braun via USRP-users <usrp-users@lists.ettus.com> wrote: > > You will need to recover the carrier frequency at the receiver. For > small errors, you can simply use a PLL for this. > > Cheers, > Martin > > On 09/15/2016 10:54 AM, Steven Knudsen via USRP-users wrote: >> Ah, excellent. I believe you are correct. If I up the frequency, the >> period reduces, so I can see more of the imposed modulation. >> >> So, forgive my ignorance, but how does one correct this? >> >> thanks very much! >> >> >> Steven Knudsen, Ph.D., P.Eng. >> www. techconficio.ca <http://techconficio.ca/> <http://techconficio.ca <http://techconficio.ca/>> >> www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen> >> <http://www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen>> >> >> /Von einem gewissen Punkt an gibt es keine Rückkehr mehr. Dieser Punkt >> ist zu erreichen. - Franz Kafka/ >> >>> On Sep 15, 2016, at 10:57, Torell, Kent <Kent.Torell@gd-ms.com <mailto:Kent.Torell@gd-ms.com> >>> <mailto:Kent.Torell@gd-ms.com <mailto:Kent.Torell@gd-ms.com>>> wrote: >>> >>> It’s a low frequency carrier error, so you are seeing the bpsk roll >>> into the other quadrature, then invert data. >>> >>> *From:* USRP-users [mailto:usrp-users-bounces@lists.ettus.com] *On >>> Behalf Of *Steven Knudsen via USRP-users >>> *Sent:* Thursday, September 15, 2016 9:50 AM >>> *To:* USRP-users >>> *Cc:* Knud >>> *Subject:* [USRP-users] B200mini and low-freq modulation of tx'd signal >>> >>> Hi, >>> >>> I have a TDMA flowgraph that defines packets using tx_time and tx_sob >>> + tx_eob. Packets are sent to a B200mini every 10 ms (which is not >>> important). Below I have the packet format from GRC followed by 3 >>> oscilloscope captures that show the effect I’m seeing. >>> >>> The B200mini is connected to an Octoclock 1 PPS reference. >>> >>> The modulation is BPSK, 2x oversampled, RRC. >>> >>> Image 1 - the GRC waveform that is input to the USRP sink >>> Image 2 - this time the transmitted signal looks pretty good. Note the >>> leading zeros so that the transmit power rises to full before samples >>> are applied. >>> Image 3 - it appears that some form of slow modulation has been applied >>> Image 4 - same again, but obviously at a different offset >>> >>> (oops, forgot to turn off stupid network config menu in scope caps) >>> >>> I am a bit stumped. A “theory” is that maybe I’m seeing a window of >>> some kind being convolved with the signal. >>> >>> <image001.png> >>> >>> <image002.jpg> >>> >>> <image003.jpg> >>> >>> <image004.jpg> >>> >>> >>> Steven Knudsen, Ph.D., P.Eng. >>> www. techconficio.ca <http://techconficio.ca/> <http://techconficio.ca/ <http://techconficio.ca/>> >>> www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen> >>> <http://www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen>> >>> >>> /Der entscheidende Augenblick der menschlichen Entwicklung >>> ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, >>> welche alles Frühere für nichtig erklären, im Recht, denn es ist >>> noch nichts geschehen. - Franz Kafka/ >>> >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com> >> http://lists.ettus.com/mailman/listinfo/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 <mailto:USRP-users@lists.ettus.com> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>