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The impulse noise requirements of the Strategic Air Command's Project 465-L data circuits, together with the requirement for alternate voice operation of these circuits, provide an opportunity to study first-circuit random noise effects in N2 carrier systems. Due to the nature of these composite services, efforts are made to achieve a level of performance that should be completely acceptable to the "military" under all known environmental conditions. Toward this end, design and operating margins have been maximized so that, under normal conditions, noise thresholds are far below actual limits. First-circuit random noise effects in N2 carrier systems are studied with particular reference to their characteristics when measured using sine-wave calibrated Western Electric 6A impulse counters and using the three-level impulse counter technique. The noise "floor" in transistorized repeaters and terminals is investigated and, based on empirical results, simple graphs are provided for estimating the random component of impulse noise and steady noise -C message weighting as a function of carrier input level and percent modulation. The transient component of impulse noise is investigated, as well as the relative susceptibility of repeaters and terminals to these transients.