Measuring television transposer intermodulation distortion

The authors examine the behavior of the intermodulation (IM) level during one line period and propose a measuring method allowing the use of a standard or a modified color-bar test signal. The latter enables the nonlinearity of the transposer to be minimized in the line synchronization region, and this is shown to minimize vision/sound crossmodulation. Differential gain and phase can also be optimized. Measurements indicate that minimization of the IM level with the three-tone method often causes unacceptable IM limits at other colors. The measurement technique is based on sampling the demodulated color-bar signal for short intervals corresponding to a selected color. This allows the simultaneous measurement of IM level at seven different points on the transposer's characteristic.<>