A tunable resonator in the gigahertz-range using circular sine-Gordon fluxons or pulsons on a lossy large-area Josephson junction with a circular impurity in the Josephson current density is proposed. To obtain steady tunable oscillations in a lossy medium, one must supply energy (''negative'' resistance). We propose to control the constant bias current with an autonomous pulson velocity-sensitive switch. One possibility for fine tuning the oscillations is to vary the strength of the Josephson impurity current. Applied Physics Letters is copyrighted by The American Institute of Physics.