Nonresonant detection of Josephson radiation from thin-film microbridges

Measurements are reported of the Josephson radiation from microbridges coupled to an X-band receiver via a nonresonant microwave transformer. Although closely coupled to the bridge, the transformer does not modify the bridge properties. We find that near the transition temperature the radiation linewidth is proportional to the square of the dynamic resistance, which is also predicted by the resistively shunted junction model. The effective noise temperature determined by the linewidth is 19 +- 3 K and the measured maximum integral power is 5 x 10-12 W