In this paper, a new improved recursive Newton-type algorithm suitable for various measurement applications in electric power systems is presented. It is used for the power system frequency and spectra estimation. The recursive algorithm form is improved with a strategy of sequential tuning of the forgetting factor. By this, the algorithm convergence and accuracy are significantly improved. To show the main algorithm features, the results of computer simulation, laboratory testing (load rejection and unsuccessful synchronization tests) and field data processing are given.