man00, Stations don't transmit their digital (HD) signals on the same channel they transmit their analog signals. The FCC assigned each station a new, separate channel for digital programming. This allows the stations to continue broadcasting their analog signal on their old channel while they are gearing up on the new channel for the transition to digital. Some of the new digital channel assignments were in the VHF band (channels 2-13), but most were in UHF (channels 14-69). KTUL, channel 8, was given channel 10 for its digital transmissions; KHBS, channel 40, was given digital channel 21, channel 5 was given channel 18, and so on. There is potential for confusion with two separate channels for each station, and the broadcasters were also concerned about their "branding" (their promos, logos, nicknames and such, their identities that had developed over years and years and were associated with their old channel numbers), and customer programming guides, etc. To help with these and probably other issues, the concept of virtual channels
was included in the digital broadcasting scheme.
HD television is transmitted to your receiver in streams of information. Data within the stream tells your receiver to associate the program you're watching not with its actual channel number, but with a virtual channel number
, an alias, instead. This virtual channel number almost always begins with the station's analog channel number, such as 8.1, 8.2 or 8.3, so people who have been watching channel 8 since 1955 can still associate the programming with channel 8, and programming guides and information sources just have to reference the virtual channel numbers. The minor part of the virtual channel number, that part after the decimal, just designates an extra channel, a subchannel, that is transmitted as part of the digital stream. Some stations transmit one or more subchannels, some don't. Channel 8 apparently has three. The actual digital channel numbers are normally unnecessary for the viewer. But sometimes, like when you need an antenna for a digital channel, or if you have to manually enter a digital channel for your receiver to search for a distant digital signal, you need the real digital channel number. KJRH in Tulsa, for example, is on analog channel 2, low VHF, but its digital signal, KJRH-DT, is on channel 56, high UHF, and a VHF-only antenna just wouldn't work for KJRH-DT.
Sorry for the confusion.