This paper presents several structures for Adaptive Notch Filters and implementation aspects of constrained ARMA models. These ANF suit very well to evolutionary spectrum analysis for sinusoidal signals in additive noise. colored or white. Several estimation algorithms may be applied with these structures (ELS,RML,RIV) and some special procedures may be imployed to increase the convergence rate, enhance the estimation consistency and reduce tha algorithm complexity. Lastly, non-stationary ANF are considered and an estimation procedure implemented.