  The $J$-matrix method is extended to difference and $q$-difference operators
and is applied to several explicit differential, difference, $q$-difference and
second order Askey-Wilson type operators. The spectrum and the spectral
measures are discussed in each case and the corresponding eigenfunction
expansion is written down explicitly in most cases. In some cases we encounter
new orthogonal polynomials with explicit three term recurrence relations where
nothing is known about their explicit representations or orthogonality
measures. Each model we analyze is a discrete quantum mechanical model in the
sense of Odake and Sasaki [J. Phys. A: Math. Theor. 44 (2011), 353001, 47
pages].
