The gain medium of a free electron laser (FEL) is a relativistic electron beam. The challenge with oscillator FELs is to decouple the electron beam from the radiation. Here we present the results of simulations and experimental measurements of a Talbot effect resonator which effectively decouples the electron beam from the radiation without the use of bending magnets. Radiation from 95 to 110 GHz can be harvested. The free spectral range is 100 MHz, though it is possible for us to remotely adjust the length and so tune between the 100-MHz resonant frequencies. The resonator also can vary the power coupled out from the resonator, allowing optimization of the power extracted from the saturated electron gain medium.