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We report characterizations of antenna-coupled hot electron bolometers designed for laboratory-based terahertz spectroscopy. These direct detectors combine sub-nanosecond response, high sensitivity, and the ability to operate below saturation when viewing a room temperature background. The optimum small-signal responsivity is 4.4 times 104 V/W, measured at a bath temperature Tb ap 0.9Tc. The corresponding saturation power is 7 nW. The saturation power increases and the small-signal responsivity decreases as the bath temperature is lowered. The measured noise equivalent power is 2.0 times 10-14 W/(Hz)frac12, near the predicted thermal fluctuation limit. The noise is white from approximately 100 Hz to 100 MHz.