Time and sample rate synchronization of RTL-SDR using a GPS receiver

Abstract

GPS receivers provide very precise Pulse Per Second (PPS) signal. A simple low cost method of time synchronization for RTL-SDR receivers using such GPS time signal is described. The PPS signal is injected into an IF stage of the RTL-SDR and detected by correlation of an expected signal shape and the measured data. The accuracy of such pulse detection algorithm is in the worst case 5 samples or up to 2.1 µs when using highest useful receiver sample rate of 2.4 MS/s. The algorithm can also be used to measure RTL-SDR oscillator offset with a very high precision for frequency corrections. The accuracy achieved is not enough for precise localization of ground targets, but it's sufficient enough to roughly estimate a location of an aircraft or a satellite.