The purpose of this paper is to present a new systematic, low cost and real-time adaptive algorithm to automatically set the loop filters parameters of the phase lock loops or delay lock loops used in synchronization systems like GPS. The aim of this method is to compute the loop filter coefficients which minimize the power of the thermal noise within the total tracking error, to improve the pseudorange measurements accuracy on each locked channel. Method is based on real-time estimations of the dynamics and signal-to-noise ratio of the incoming signals, which are used to compute the better compromise between the equivalent noise bandwidth and the steady state error factor of the loops. Estimates of signal parameters are obtained in real-time from observations of the error signal delivered by the dicriminator. From these estimates and from the knowledge of the equivalent linear model of the loop, an optimization function is built that gives the pole position of the loop transfer function that minimizes the equivalent noise bandwidth keeping a fixed probability that the error signal becomes greater than the lock threshold. This solution is evaluated by an iterative method with an update rate of 50 Hz or less, depending on the velocity of the variation of the dynamics and on the hardware constraints. The Fast Adaptive Bandwidth Lock Loop (FAB-LL) results in a real-time optimal use of the loops because it minimizes the power of the pseudorange measurement thermal noise with respect to the imposed error due to dynamics. Practical and theoretical approaches have shown the method is operational and robust.