Abstract: A doppler/range simulator for use in testing aircraft systems based on the rinciple that an ionized gas absorbs microwave radiation and thus becomes raised to higher energy levels, and when falling back to the original energy state the ionized gas re-radiates the absorbed microwave energy. A frequency control simulates a doppler or velocity signal. A voltage or current control simulates the time delay or altitude range signal.The test set is in the form of a light-weight anechoic chamber lined on the inside with energy absorbant material except for the top. Within the enclosure there are positioned near the open top a plurality of parallel - arranged flurescent tubes adapted to be energized with pulsating d.c. to produce a flow of ions in the tubes which flow from one end of the tube to the other. The tubes are excited in parallel so that the ion flow is always in the same direction.