I was using a dongle with r820. juha
> On May 25, 2016, at 23:27, Piotr Krysik <per...@o2.pl> wrote: > > Juha, > > What type of demodulator did you have in the dongles used for the test? > > -- > Piotr > > W dniu 25.05.2016 o 14:46, Juha Vierinen pisze: >> In my testing, this phase rate difference seemed constant and I could >> simply calibrate it out by looking at the phase rate term estimated >> from the phase of the cross-correlated noise. The samples stay aligned >> for hours, so the issue is caused by the tuner or the DDC. One theory >> that I had was that the multi-rtl driver somehow sets up the dongles >> differently, but I never got around to looking at the code. >> >> I think this was the script I used to figure out what the phase drift was: >> https://github.com/jvierine/chirpsounder/blob/master/apps/passive_radar/rnoise.py >> >> Here's the IQ plot to prove that the cross correlated phase is stable >> over 6000 seconds: >> >> http://kaira.sgo.fi/2013/09/16-dual-channel-coherent-digital.html >> >> juha >> >> On Wed, May 25, 2016 at 12:14 PM, <jean-michel.fri...@femto-st.fr >> <mailto:jean-michel.fri...@femto-st.fr>> wrote: >> >> From our own experience with dual-dongle measurements, the phase drift >> seems to be strongly related to R820T(2) temperature. We reduced >> significantly >> the phase drift by gluing a large heat sink common to both chips >> on both >> dongles, without completely removing this effect (we aim at >> measurements lasting >> multiple hours). At the moment the only option we could think of >> (mail to this >> mailing list dated 28 May 2015) is switching to a reference clock >> to calibrate >> for the phase difference between the local oscillators, but the >> actual cause >> of the drift remains a mistery (probably due to the implementation >> of the PLL, >> but I cannot understand why Phase Locked Loops would drift in >> Phase !). >> >> JM >> >>> It wouldn't be as simple as it was for me as a developer and as it >>> (hopefully) is for the end user without your hardware mod. >>> >>> Can you say something more about the residual center frequency >>> difference? Where might it come from? I prepared little test of >>> coherency between the receivers >> (multi-rtl/examples/test_multirtl.m). >>> Among all the figures that it shows there is a plot of relative >> phase >>> offset of signals coming from the receivers. In fact I have seen >> linear >>> phase change on that plot - that corresponds to some central >> frequency >>> offset. If I know what is the source of this offset maybe I will >> be able >>> to find some way to fix it in software. >>> >>> -- >>> Piotr >>> >>> W dniu 25.05.2016 o 08:24, Juha Vierinen pisze: >>>> This is awesome! I'll definitely try this out soon. I use one off >>>> python scripts to find the sample offset and the small >> residual center >>>> frequency difference. This simplifies the process significantly. >>>> >>>> This should make it much easier to implement a passive radar >> block, or >>>> an interferometry block. >>>> >>>> juha >>>> >>>> On Tue, May 24, 2016 at 4:03 PM, Piotr Krysik <per...@o2.pl >> <mailto:per...@o2.pl> >>>> <mailto:per...@o2.pl <mailto:per...@o2.pl>>> wrote: >>>> >>>> Hi all, >>>> >>>> I want to announce new GNU Radio related project prepared >> by me - >>>> Multi-rtl: >>>> https://github.com/ptrkrysik/multi-rtl >>>> >>>> It is a Gnu Radio block that combines multiple RTL-SDR >> receivers into >>>> one multi-channel receiver. >>>> >>>> Only hardware modification to RTL-SDR dongles required is >> connecting >>>> them to a common clock source (i.e. one of the dongles' >> oscillator as >>>> Juha Verinen showed once). Each channel can work on a >> different >>>> central >>>> frequency. >>>> >>>> Everyone who wants to know how it was achieved is invited >> to read my >>>> github page: >>>> >>>> https://ptrkrysik.github.io >>>> >>>> Best Regards, >>>> Piotr Krysik >>>> >>>> _______________________________________________ >>>> Discuss-gnuradio mailing list >>>> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >> <mailto:Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org>> >>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> -- >> JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de >> l'Epitaphe, 25000 Besancon, France > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
