  Josephson oscillations generated by a SQUID were used to measure photon
assisted tunneling in a superconducting single electron tunneling (SET)
transistor. The SQUID was fabricated only a few microns from the SET
transistor. The close proximity of the generator to the SET transistor allowed
for a continuous sweep of the excitation frequency from 10 GHz to 190 GHz. The
amplitude of the Josephson oscillations were tuned by adjusting the flux
through the SQUID loop while the frequency was independently adjusted by
controlling the bias voltage across the SQUID. Current peaks which could be
attributed to photon assisted tunneling in the SET transistor were observed for
bias voltages less than 4*Delta/e.
