  Unbound interacting compact binaries emit gravitational radiation in a wide
frequency range. Since short burst-like signals are expected in future
detectors, such as LISA or advanced LIGO, it is interesting to study their
energy spectrum and the position of the frequency peak. Here we derive them for
a system of massive objects interacting on hyperbolic orbits within the
quadrupole approximation, following the work of Capozziello et al. In
particular, we focus on the derivation of an analytic formula for the energy
spectrum of the emitted waves. Within numerical approximation our formula is in
agreement with the two known limiting cases: for the eccentricity {\epsilon} =
1, the parabolic case, whose spectrum was computed by Berry and Gair, and the
large {\epsilon} limit with the formula given by Turner.
