I cleaned up the patch a little and applied it to my tree. I can't vouch for the precision, but it builds, runs and doesn't seem to set any small animals on fire.
The revised commit is at https://github.com/keenerd/rtl-sdr/commit/f2328161ea And a windows build is at http://igg.kmkeen.com/builds/rtl-sdr-mingw32-v0.5.3.r32.gf232816.zip I am a bit curious about the sigma-delta-mod math. We've got three different sdm calculations now. The one in osmocom's repo, this new one from O. Jowett and M. Bavaro's version (http://michelebavaro.blogspot.com/2014/05/gnss-carrier-phase-rtlsdr-and.html). -Kyle http://kmkeen.com On 8/23/14, Oliver Jowett <[email protected]> wrote: > Hi > > I've made some changes to the R820T tuner code to improve the tuning > precision. > The old code lost some precision to rounding errors etc, causing an > unpredictable frequency-dependent tuning error over and above the limits of > the hardware itself. > > The changes are in a github pull request here: > https://github.com/steve-m/librtlsdr/pull/10 > (but the rtl-sdr page suggests I mention it here too, so here I am) > > I've attached some graphs showing the results of these changes. These are > showing what happens to the apparent frequency of a nominally fixed > external signal (the GSM FCCH tone measured by kalibrate) when the tuner > frequency is changed. In an ideal world you'd expect that the apparent > frequency offset would change in lockstep with the tuner frequency; > anything different is tuner imprecision or oscillator drift. > > At 954MHz these changes improve the tuning precision from approx +/-750Hz > to +/-200Hz. > > Oliver >
