Development of a practical method of measuring the modulation depth of the NTSC television visual carrier

Cable television systems in the United States use tens-of-thousands of NTSC modulators to modulate television programming for use by their customers. Proper operation of these modulators requires careful adjustment of the controllable output parameters of these modulators. The output parameter discussed herein is the modulation depth of the visual carrier. Until now, little effort has been spent on developing an easy method of determining the modulation depth. Research of modulation measurement methods reinforces this statement. Background material is covered and used to develop a measurement strategy. A circuit realization follows this development. A prototype of this circuit is constructed and tested. The test results are very encouraging. Although there are accuracy limitations in this particular circuit, the validity of the measurement method is reinforced.