  Hamiltonian reduction is used to project a trivially integrable system on the
Heisenberg double of $SU(n,n)$, to obtain a system of Ruijsenaars type on a
suitable quotient space. This system possesses $BC_n$ symmetry and is shown to
be equivalent to the standard three-parameter $BC_n$ hyperbolic Sutherland
model in the cotangent bundle limit.
