The frequency spectrum analysis of RF signals has been become a key technology in modern electronic countermeases. Acousto-optics frequency spectrum analyzer is very prospective for its performance. To detect all information carried by the RF signals including amplitude

frequency and phase

and to increase significantly the dynamicr ange

the scheme of AO(Acousto-optics) heterodyne frequency spectrum detection has to be used. In this paper

the principle and realization of a sort of AO heterodyne detection receiver are reported

and especially the method of calculating sensitivity has been discussed in detail which has been proved highly effective by our prototype receiver.The feature of the AO prototype receiver are as follows:The dynamic range ≥50d Bfrequency resolution 2Hz bandwidth 20MHz central frequency 140 MHz.