Typically separate tuners in the TV - which one is used depends on your selection of 'air' or 'cable'...
is the American standard for analog television, otherwise known as 480i. (No longer avaialble as 'over the air' channels - but some old devices that require you to set the TV to channels 3 or 4 would still use this...)
This would be used during the 'analog' portion of channel scan when input is set to 'Air' - and not likely to find any...
is the new digital standard taking place in North America that encompasses a digital form of NTSC video (480i) as well as other forms of video (720p, 1080i, etc).
This would be used during the 'digital' portion of channel scan when input is set to 'Air'.
is a modulation scheme that allows the TV to access and display unscrambled
digital cable TV without using the cable box.
This would be used (if available) during the channel scan when input is set to 'Cable'.
All TV's manufactured since March 2007 and entering the US market are required to have an ATSC tuner - doubt even Thor has stock older than that...
No requirements like that for QAM - so buyer beware...
Of course NONE OF THIS MATTERS if you are using a cable/satellite service with a 'box' provided by the company... You are bypassing all tuners and likely feeding in through component or HDMI inputs.
If your provider scrambles the signal - no tuner will work - you will need a 'box' from the provider.
The tuners only come into play when receiving over the air (ATSC) or cable without a 'box' (QAM needed for digital cable systems).