[GroundUrMast]

The VHF spectrum (low band, CH-2 through CH-6 and high-band, CH-7 through CH-13) is still reserved/allocated/assigned to broadcast television. Because there is more RF interference in that spectrum, many broadcasters elected to move their operations to UHF assignments as they switch to digital operation. Not all chose to do so though.

Because the low-VHF channels are subject to the most interference, you'll find few full service broadcasters electing to use real CH-2 through CH-6. Still, a few exist. Most stations using the low-VHF spectrum are low power stations, either fill-in translators or small independent broadcasters.

Back in the 80's, the cell phone industry started operation on the frequencies formerly reserved for UHF channels 70 through 83. Then in the recent transition from analog to digital TV broadcasting, the FCC re-allocated UHF channels 52 through 69 to various services including cell, broadband wireless and others.

So, back to real vs. virtual channels, a digital TV needs to keep a list of real channels that have an active signal available, and, the TV also needs to keep track of the separate programs available in each real channel. Digital broadcasting technology now allows a broadcaster to send up to five video channels in standard definition.

When you punch in "4", "-", "2" on the remote here in Seattle, the TV has to look in the table created during the channel scan. It finds an entry for virtual channel 4-2 and sees that the real channel is UHF CH-38. The tuner is then set to real channel 38 and the data associated with the desired program can be filtered out of the rest of the data and set to the video and audio decoding process.

Many sets will not tune or display a channel without performing a channel scan... to create the table data that is used to control the tuner.

Some of my sets will accept manual entry of the real channel number. If there is a valid signal present, the set is smart enough to add the new information about the real & virtual channels so that in the future, I can channel surf or punch in the virtual channel number.