Like Compressing Apples and Oranges

You're so accustomed to talking about HDTV, but did you stop to think about some of the early work? Here's a snippet from Ron Wolf's article (29 Dec 1982; The Miami Herald):

Broadcasting and cable executives are suddenly talking about another gadget that is likely to have a profound effect on the business: a device that is able to "squeeze" two television signals into one channel.

General Electric unveiled these electronic components last month that are part of a "bandwidth compression system"--meaning they will double the channel capacity of a cable system.

GE accomplishes this technical feat by electronically dissassembling the 525 lines that make up a television picture. Every other line is eliminated and replaced by a corresponding portion of a second picture. The resulting composite is then transmitted as a single TV signal.

After the signal is received in the home, the two images are electronically separated.