This is a different DACS than the telecom one. This recovers and manages date from the vertical interval of the NTSC video system. PBS encoded data at the satellite head end, and member stations selectively downloaded and trafficked the data according to various national contracts (like the VISA card hot-list). System was also used for inter-network communication in the pre-internet days.
Hadn't touched this thing in 15 years or so, but it booted right up. Don't have a manual, but I do have devices that can encode VBI data. This device was made by EEG, who also made the first closed caption encoders. It's the product of engineers leveraging the data-carrying capability of the vertical interval.
And yeah, 6s rocks because it's the last of the real headphone jacks. Dangit.
