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
