Manual Tuning
Each digital OTA channel number is composed of a main number and a subchannel, for example 4.1, 4.2, etc. A dash is an alternate form of representation: 4-1, 4-2... The dot and dash are interchangeable; they both mean the same thing. The main channel numbers refer to the same radio frequencies as previously. However, now "virtual channel" (technically known as logical channel number) numbers are common. So, Channel 4 digital signals may now actually be broadcast on channel 43, or any other frequency. When the ATSC tuner does a channel scan, it finds the signal on channel 43, learns that this material is called "Channel 4", and remembers that mapping. The user can tune to "4", and the tuner will know to tune in 43. Before a scan is done, it may be possible to access the programs directly by manual tuning, by entering 43-1, 43-2... After the scan, the programs would usually be accessed by entering 4-1, 4-2 etc., but it may still be possible to also access them directly at 43. If stations change their broadcast frequencies, it may be possible to access the new frequencies directly, but the usual procedure is to rescan all of the channels.
A complete table of US station assignments is here: Tentative Digital Television (DTV) Channel assignment
The actual channel frequencies are listed here: Television Frequency Table
Read more about this topic: ATSC Tuner
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