  The design and performance of an electron spin resonance spectrometer
operating at 3 and 9 GHz microwave frequencies combined with a 9 T
superconducting magnet is described. The probehead contains a compact two-loop,
one gap resonator and is embedded in the variable temperature insert of the
magnet enabling measurements in the 0- 9 T magnetic field and 1.5-400 K\
temperature range. The spectrometer allows studies on systems where resonance
occurs at fields far above the $g$ $\approx 2$ paramagnetic condition such as
in strongly interacting spin systems. The low quality factor of the resonator
allows time resolved experiments such as e.g. longitudinally detected ESR. We
demonstrate the performance of the spectrometer on the MgB$_{2}$ superconductor
and the RbC$_{60}$ conducting alkaline fulleride polymer.
