An impulse technique for determining radiation impedance and radiation directivity of jet nozzles is discussed. Results for an unflanged pipe are compared with the theoretical results of Levine and Schwinger [Phys. Rev.73, 383–406 (1948)] for the purpose of justifying the technique. Data are then presented to show the effect of nozzle size and jet velocity on both nozzle transmission and radiation impedance and radiation directivity. Conical nozzles are used and the results for 2‐ and 1‐in. diameter nozzles are compared with those for the 4‐in. diameter straight unflanged pipe. Effects of jet exit velocity up to 1300 ft/s are displayed and discussed in the light of available theory. Spectral energy is determined for the incident and reflected wave signals in the pipe, and the transmitted wave in the farfield and energy conservation for the system is discussed. Finally, it is shown that the test method can be usefully applied at frequencies above the plane mode regime.