This paper has analysed several important zero subsets of the extended FT of finite length signal. With Hadamard factorization theorem

several theorem are developed to expose the relationship between these zero subsets and FT spectral magnitude or phase. The results for reconstruction of discrete finite length signal from FT spectral magnitude or phase are further extended for that of continuous signal

and both are expressed in a unified form by the zero set of the extended FT. In addition

a new result for reconstruction of mixture phase signal from FT spectral magnitude is obtained.