Abstract: Modulators for producing a composite video signal comprising composite video color bars of one volt, peak to peak, of the United States NTSC standard type, are described. The modulators include an EPROM matrix coupled to receive the outputs from a video graphics circuit and programed to produce the color bars from such outputs. The modulator also has a decoder interposed between a loop returning the output from the EPROM matrix to the video graphics circuit and thence to an output driver producing an output of color bars at one volt peak to peak into a 75 ohm load.