A simple method of simulating the variation in the amplitude of microwave signals from rocket-borne transmitters is presented. The technique reproduces signal changes caused by vehicle motion as well as those induced by plasma effects. The simulator uses a voltage controlled attenuator which is programmed to vary the output power of a test transmitter to produce the variations in signal amplitude which would be observed during a flight. An analog system which is suitable for variations of simple cyclical shape and a digital simulator which can reproduce changes of any complexity are presented. Use of the simulator before flight allows the dynamic behavior of a microwave link to be determined, permits optimum receiver and recorder parameters to be selected, increases operator confidence, and enhances flight test reliability. (Author).