Weird Television Channel with black screen and white Wavelength/Sonar/Radar Graph When I was a Kid?

When I was about 7 or 8 years old (1997-1998) I had an old Television in my room with Time Warner Cable in Houston, Texas. I remember I would flip through channels being bored. One thing has always puzzled me though. After I got ped channel 78 I would hit about 15 or 20 channels of white noise, and then there was this odd channel. It was a black screen with white text, almost like an old pre-windows computer. There was a white graph that measured some kind of wavelength. As a kid, it reminded me of like a heart monitor. But looking back it was more like an active wavelength or soundwave graph. Does anyone have any idea what it might have been?