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
