  We present a straightforward discretization of the Bessel functions $J_n(x)$
to discrete counterparts $B^{(N)}_n(x_m)$, of $N$ integer orders $n$ on $N$
integer points $x_m \equiv m$, that we call discrete Bessel functions. These
are built from a Bessel integral generating function, restricting the Fourier
transform over the circle to $N$ points. We show that the discrete Bessel
functions satisfy several linear and quadratic relations, particularly Graf's
product-displacement formulas, that are exact analogues of well-known relations
between the continuous functions. It is noteworthy that these discrete Bessel
functions approximate very closely the values of the continuous functions in
ranges $n + |m| < N$. For fixed $N$, this provides an $N$-point transform
between functions of order and of position,$f_n$ and $\widetilde{f}_m$, which
is efficient for the Fourier analysis of finite decaying signals.
