Within their signal, digital stations send channel remapping info via something called "PSIP". PSIP stands for "program and system information protocol" -- see here for more info : http://www.psip.org/
. Note that stations can, and do send quite a bit more info besides virtual channel remapping info via PSIP, such as Time/date info as well as Electronic programming guide.
In most cases, the virtual "remapped channel" number is the channel you will see displayed on your TV, when you tune to a local digital/HD station, and in most cases is the channel you'll tune to in order to watch that station.
In most cases, in discussions on AVSforum the virtual, "remapped channel" number is usually what we use when we list digital station channel numbers, and is also what is referred to in the "channel" column in your results for your location at www.antennaweb.org
Virtual channel remapping via PSIP allows stations to keep the channel branding which exists for their current, analog station even though the actual channel* the digital station is broadcasting on is different currently, or may be a different actual channel number after analog shut off occurs. It also allows viewers to use the same channel number for the digital station they are used to using for the analog station.
* - For more info See 8. Is a station's digital signal transmitted on the same channel as its analog signal?
An important thing to remember is that the "remapped channel" is a "virtual channel" and has nothing to do with the actual channel/frequency the digital station is broadcasting on. Therefore even though it may appear when you tune to say, channel 4.1 that you are tuning to a VHF channel, the station may actually be broadcasting on a UHF channel/frequency and the tuner in your receiver/set is actually "tuning" not to channel 4, but to the actual channel the station is broadcasting on, even though it displays "4.1" on the screen.
For example, WNBC-DT(digital) New York, NY remapped channel is 4, although WNBC-DT actually transmits on UHF channel 28(554~560 MHZ).
Also, with Digital TV, "remapped" channels are displayed in the following format :
[ X.x ] X = Major remapped virtual channel number, and x= minor remapped virtual channel number .
A station will have one major remapped channel number, and, with multicasting can run several different program services on several different minor channel numbers. For example, WNBC-DT New York has the following remapped virtual channels :
4.1 for NBC/NBC HD/WNBC programming
4.2 for NBC "weather Plus"
In most cases the remapped major channel number will be the same as the analog station's channel number. For example, WNBC-TV(analog) transmits on VHF channel 4(66~72MHZ), WNBC-DT(digital) remapped major channel number is also 4, even though the digital station actually transmits on UHF channel 28(554~560MHZ).
One problem with virtual channel remapping is that an OTA only DTV receiver must be getting a "good enough" signal to acheive a signal lock from the station in order to receive the PSIP information from the station in order for the channel remapping to be accomplished. So, in some cases it can be difficult, and cumbersome, to adjust the antenna for reception of different stations while only using the "autoscan" feature of the receiver to "find" stations in your area. However, luckily, most, if not all receivers do have the capability to allow the user to either :
#1).Tune manually directly to the channel the station is actually broadcasting on via "direct acess tuning".
#2). Access a "channel edit" screen that will allow you to manually select actual channel numbers for broadcast stations in your area so that the PSIP info from the station will be "saved" when you achieve a signal lock on the station of interest.
#3) Via a menu option, to specify the Actual channel number the station is broadcasting on in order to "scan in" the station so you can view the signal meter on the receiver while adjusting antenna accordingly, or an option that will allow you to add/scan in a number of "new" channels without deleting previously "scanned in" channels.
It is often necessary to have these options not only for adjusting your "rabbit ear" antenna, but also so you will be able to "scan in" stations in different directions from your location given for example, the use of a directional antenna with rotor.