About 30 percent of the cable systems in the United States use Harmonically Related Carrier frequency, which is different from air-transmitted television signals and from the remaining 70 percent of cable systems. HRC reduces interference when many channels are transmitted over cable. Most television receivers that are labeled "cable-ready" are compatible with HRC.
Macintosh TV, however, cannot receive an HRC signal -- because each channel's frequency is shifted down by 1.25 MHz from the standard channel frequencies recognized by Macintosh TV.
Solution: A New Control Panel
A revised TV Setup control panel that allows Macintosh TV to pick up the HRC frequency will be available starting November 30, 1993. It can be downloaded from the Apple Software Updates web site at http://www.apple.com/swupdates.
This new control panel also fixes a problem that would sometimes cause the screen to darken after returning from TV mode.