Would either of these issues in the rtlsdr driver consistently tune the two dongles on slightly different frequencies, even if you ask them to tune to exactly the same frequency? This is what the problem seems to be.
juha On Wed, May 25, 2016 at 10:35 AM, <mle...@ripnet.com> wrote: > There are a couple of issues with the rtlsdr driver used by gr-osmocom in > this regard: > > > > (A) The charge-pump loop current is too constrained for the higher > frequencies > > (B) The "dither" option appears to have a bias that causes a (small) > frequency offset. > > > > The driver that AirSpy uses fixes both of these, although without > "dither", the tuning granularity is worse. Not sure this matters. > > > > > > > On 2016-05-25 09:28, Marcus Müller wrote: > > That, or simply, the output clock VCO changes its reaction to the > control voltage under certain circumstances (temperature, frequency) so > much that the control loop loses the ability to reach stationary > exactness (e.g. due to natural limits on the magnitude of the VCO > voltage). These devices definitely were made with cost in mind – not > with maximum reliability, and hence I can believe that for example with > the Elonics E4000 tuner, the charge pump used to generate the VCO > voltage simply might deteriorate with temperature. > > Cheers, > Marcus > > On 25.05.2016 14:25, Sylvain Munaut wrote: > > Hi, > > 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 !). > > If the phase comparator is digital ( i.e. a XOR ) and the input clock > is somewhat analog, the gate thresholds might vary depending on > temperature, thus shifting the cycle a bit. > > Just a thought. > > Cheers, > > Sylvain > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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