From The TV IV
A virtual channel is a channel number as displayed on digital television tuners which, for the largest part, is different than the station's channel on which they broadcast their digital signal physically. It is displayed through a process called Program and Station Information Protocol (PSIP) and is the original channel number the station used under analog broadcasts. The "virtual channel" was put in use to keep viewers from being confused about where their local over-the-air TV stations would be after the analog shutoff. If a station's physical digital channel is entered into a digital tuner, it will display as the virtual channel automatically. For example, if a station that had been on analog channel 6 is broadcasting its digital signal on channel 28, it will show up on tuners as 6 even if 28 is entered.
The digital broadcast spectrum encompasses channels 2 to 13 VHF and 14 to 51 UHF. Somewhere down the line, channels 2 through 6 will be eliminated from VHF. As part of the digital protocol, channel designations are posted as the physical number suffixed by either .1 or -1. The virtual channels are identified similarly. Through PSIP, the virtual channel displayed can go from 01 to 999. Stations' subcarriers are displayed, both physical and virtual, under suffixes .2 or -2, .3 or -3, and so on. The .1 or -1 on the primary channel does not have to be entered but the subcarrier suffixes must be entered to see them. Surfing with a remote control for a converter box or an ATSC television will allow seeing all available over-the-air channels. VHF and UHF have no relevance to virtual channels.