Why do customers with high-definition digital TVs need set-top boxes for digital cable service?
Set-top boxes make cable carriers service compatible with customers TVs. Cable providers use a different scheme, QAM (quadrature amplitude modulation) than terrestrial broadcasters such as PBS, and ABC, which use ATSC (Advanced Television Systems Committee) to transmit digital signals. Also, cable providers scramble signals on most of channels. Which cable customers do not need a set-top box? Only those customers that both: • Subscribe to a basic cable TV package of only terrestrial channels. (These comprise national broadcasters such as ABC, NBC, CBS, PBS, and Fox plus local access channels, which broadcast for example, town meeting sessions, public school shows, and local town programs.) These channels are not scrambled. • Have advanced high-definition televisions with QAM tuners. Customers can either check their TV documentation or contact their TV manufacturer to find out if they have QAM tuners. Not all high-definition televisions have QAM tuners. What about the 14% of people with
