A simulator for Doppler VOR signals includes sources for carrier frequency (1), 30 Hz reference frequency (2), variable phase 30 Hz frequency (3) and baseband frequency (4). Programmable read only memories (PROM's) (8a, 8b) control up/down counters (5a, 5b) to generate antenna phase jump functions which in turn drive sinusoid function generating PROM's (6a, 6b) the outputs of which modulate a proportion of the carrier frequency to generate simulated upper and lower sidebands. The sidebands are further modulated by outputs by PROM's (20a, 20b) which impose blending laws on the sidebands before the sidebands are combined (25) with the rest of the carrier and the 30 Hz reference signal. The variable phase 30 Hz signal controls a phase locked loop including counters (17a, 17b) from which stepping control signals are derived for the phase jump PROM's. IMAGE
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