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This paper analyzes the effects of jitter on the GPS and Galileo navigation signals. Jitter effects have usually been modelled as additive noise, based on a sinusoidal input signal, and limits the achievable Signal-to-Noise Ratio (SNR). Analysis shows that psec-level jitter specifications are required in order to keep jitter noise well below the thermal noise for software radio satellite navigation receivers. However, analysis of a BPSK system shows that large errors occur if the jittered sample crosses a data bit boundary. Quadrature Phase Shift Keying (QPSK) modulation achieves greater bandwidth efficiency than BPSK. The new GPS L5 signal is QPSK modulated. The Binary Offset Carrier (BOC) spreading modulation has recently been recommended by GPS-GalileoWorking group on Interoperability and Compatibility for adoption by Europe's Galileo program for its Open Service (OS) signal at the L1 frequency and by the United Sates for its modernized GPS L1 Civil (L1C) signal. BOC signals have more transitions and hence jitter creates more woes. The aim of this paper is to derive expressions for noise due to jitter taking into account the transitions probability in QPSK and BOC systems. Both simulations and analysis are used to give a better understanding of jitter effects on Software Radio GNSS receivers.