QAM Math Cliff Note Sheet

750 MHZ Cable System offers cable systems typically 33 digital slots/channels with allow one QAM modulator per 6 MHz channel.  How many channels within each digital slot/channel is the part of the math problem we should have been asked during word math problems in school.

An 860 MHZ Cable System offers cable systems typically 51 digital channels with allow one QAM modulator per 6 MHz channel. Some long time cable personnel may refer to the 6 MHz channel space as an EIA channel as that was the nickname for analog channels for many years.

Keep in mind operators need to offer many other services within their cable plant such as cable modems and telephone services which take valuable bandwidth away from offering more 'tv channels' via analog or digital mode. So an 860 MHz system doesn't have 135 available channels if you do the math of 6 divided into 860 after you take away the reverse channels.

Each digital channel of available 6 MHz bandwidth that has a QAM modulator outputing 38.8 Mbps to customers. The operator has to decide how much bandwidth of each program service or channel that each SD or HD service can use. If a typical SD program service/channel uses 3.75 Mbps you can get 10 channels into each QAM digital slot/channel. 

SD Channels

3.75 Mbps divided by 38.8 = 10 digital program channels                              3 Mbps divided by 38.8 = 12 digital program channels                                  2.5 Mbps divided by 38.8 = 15 digital program channels

HD Channels

19 Mbps divided by 38.8 = 2 HD channels per QAM                                     12 Mbps divided by 38.8 = 3 HD channels per QAM                                         9 Mbps divided by 38.8 = 4 HD channels per QAM