1981-00-00 National College Television was launched.
1981-00-00 WTBS satellite feed was split from its terrestrial signal; but all of the shows seen on WTBS continued to air on its satellite feed; the difference? National advertisers replaced the local ads on the satellite feed.
1981-00-00 The Movie Channel began broadcasting movies in Stereophonic audio, made possible with the cable companies' FM cable service. HBO began their stereophonic audio service years before.
1981-04-12 ARTS (Alpha Repertory Television Service) was launched; it shared with Nickelodeon 9pm-3am ET. It was a joint venture between the Hearst Corporation and the American Broadcasting Company.
1981-05-28 Spotlight (PAY) was launched as a 12-hour service, went 24 hours in 1982.
1981-06-05 Night Flight premiered on USA Network as an weekend overnight programming block (11pm-3am ET, expanded to 7am ET later).
1981-07-04 American Educational Television Network might have moved to another transponder slot on this day (it shared with Showtime West until Showtime went 24 hours every day), or it stayed there for a few months while cable systems using the Showtime West feed switched to the Showtime East feed Mon-Fri from 3:30am until 12:30pm Pacific Time. I don't know which was which for sure. I'm guessing AETV was on that transponder for a few months and it either moved or folded soon after.
1981-07-04 Showtime went 24 hours a day. For the time being, the Western feed for Showtime used the Eastern feed from 3:30am-12:30am Mondays through Fridays and showed the Eastern feed's 3:30am-6:30am feed from 12:30pm-3:30pm due to issues that are not known yet, but later on, the Western feed's lineup would be fixed up to show the entire Eastern feed on a three-hour delay as standard practice for Western viewers.
1981-00-00 The Consumer News and Consumer Shopping Guide is launched by Vector Enterprises. It features 100 alphanumeric frames to research local supermarket prices each week and centrally assembles the information for national distribution on a system-by-system basis.
1981-08-01 MTV (Music Television) was launched with the first video: The Buggles with "Video Killed the Radio Star."
1981-08-15 EWTN (Eternal Word Television Network) was launched.
1981-09-00 CBN Satellite Service was renamed CBN Cable Network.
1981-09-00 Channel 33 Tijuana signed on.
1981-09-00 HBO went 24 hours a day on weekends.
1981-10-12 CBS Cable signed on.
1981-11-00 FNN (Financial News Network) debut as a broadcast affiliate feed for stations such as channels 18 and 48 in Los Angeles and San Diego respectively as well as for some cable operators.
1981-11-06 PRISM New England signed on (became Comcast Sports Net New England in later years.)
1981-11-20 Satcom 3R satellite was launched.
1981-12-00 a short-lived subscription TV service advertised in Tuned In San Diego magazine. It is unknown whether it was on a UHF TV station.
1981-12-12 K26AC, the first LPTV station, signed on in Bemidji, MN. It went pay-TV (SelecTV) part-time at any time during the day.
1981-12-17 Modern Satellite Network was last seen on the HBO west feed transponder slot as HBO went 24 hours a day everyday beginning that Monday. It's unknown if it was seen on another transponder.
1981-12-28 HBO begins broadcasting a 24 hour a day schedule.
1981-12-32 (sometime after Dec 12) Low Power (K48AL) Channel 48 (relaying channel 18 in San Bernadino) signed on in Poway/San Diego. It was announced to be a new station on May 12, 1980. The FCC granted a licence to cover on December 10, 1981.