After sampled it for half or full window width and applying the mathematical transforms like Fourier, Valse, Hartley etc to find suitable accuracy…..

Bhupendra Desai, thanks a lot for your answer. Yes, I know that it is related to Fourier transformation, but please, if you can, be more detailed in your answer. Specific conditions of my question related to situation when the period of the beating frequency between Fs and Fo takes hundreds or thousands samples, so it have to be processed correctly. How? This is the question.

Recovering the shape of a periodically sampled signal can be done using a process called interpolation. Interpolation is a method of estimating values between two known points by using mathematical functions. In the case of a periodically sampled signal, interpolation can be used to estimate the values of the signal between the points of the periodic samples. This can be done by fitting a curve to the sampled points and then using the curve to estimate the values of the signal at other points. There are several methods of interpolation that can be used, such as linear interpolation, cubic spline interpolation, and polynomial interpolation.

Thank you, Rana Hamza Shakil

I added an illustration of a periodically sampled sinusoidal signal with CONSTANT amplitude and phase when the sampling frequency is close to the signal frequency.

In real conditions signal can be non-sinusoidal, so how recover its shape in such a situation? Simple interpolation doesn't help.