In North America there are very few NTSC broadcast (analog) stations still in operation. Full power NTSC stations in the US went dark in 2009 and Canada in 2011.
Since the DMR-ES20 doesn't tune digital signals, ATSC (antenna) or clear QAM (cable), the most useful connections are through line inputs, composite yellow video plus white/red audio or S-Video plus white/red audio, fed from external tuning devices such as ATSC tuners/converters, cable converters or satellite receivers.
If your DMR-ES20 receives it's signal through a composite video or S-Video line input a channel scan will not find any channels.
If your DMR-ES20 is running a channel scan from a coax cable (RF) connection there will be just one channel, usually channel 3 (or 4), depending upon the output channel of whatever external tuning device you are using.