Noise studies of both the dc and ac Josephson effects have been performed on a high‐Tc ramp‐type Josephson junction irradiated at 176 GHz. Well‐established analytical results for noise in overdamped RSJs are used to model the measured I‐V characteristics, and their agreement is excellent. Noise‐rounded I‐V curves at the critical current and the first and second Shapiro steps under coherent 176 GHz radiation have been studied in detail at several temperatures and rf power levels. The noise temperatures inferred from these simulations are close to the physical temperatures. An increase of noise temperatures at high radiation power levels is a result of radiation heating, which could be due to a bolometric effect.
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