Abstract: A reference signal generator is controlled by a central processing unit (20) via a multibus interface (22, 24, 26) and includes a plurality of signal channels (2, 4, 6, 8) selectively responsive to external signals (E.sub.c, E.sub.m) or internally generated signals (I.sub.c, I.sub.m2, I.sub.m4, I.sub.m6, I.sub.m8) for providing carrier (12), modulating (16), or amplitude modulated (34) output reference signals (E.sub.o2, E.sub.o4, E.sub.o6, E.sub.o8) having a variety of waveforms. One of the signal channels (8) is arranged to sum the outputs of the other channels. Each of the channels includes an output attenuator (44, 46, 48, 50, 52, 56) which imparts a relatively high resolution to the output reference signals (E.sub.o2, E.sub.o4, E.sub.o6, E.sub.o8) and a circuit (54, 60, 62, 64, 66) which adjusts the range of said output reference signals. A built-in test capability (FIG. 3) is provided which permits selection and testing of the output reference signals from any one of the channels (2, 4, 6, 8).