[N9ZQA]

The switch to digital only affects BROADCAST television. Cable companies are not required to switch to digital transmission, although some are taking advantage of the media hype over DTV to move in that direction.

I'm not sure what the regulations are regarding the use of the -DT suffix on a station's callsign.

"Digital cable" uses QAM modulation instead of 8VSB as ATSC does for over-the-air transmission. You are correct in that digital cable viewers require a set-top box to decode the digital signal to either RF, composite video, or some other form of display interface technology - the same as using the converter box to receive over-the-air broadcasts.

As I understand it, the analog feeds on the cable of the local channels are done with a slightly heavier-duty version of the set-top converter boxes we've come to know and love. There may be other methods, but I'm not aware of any at the moment. Would love to hear if anyone has further info.

However, since cable television is brought to you on - just that - a cable, there is no requirement for them to use either analog or digital. The signals transmitted down that cable do not exist to the outside world (at least on a good day), so the cable company can send digital signals as well as analog NTSC signals. The advantage to them is that they can pack multiple digital signals into the bandwidth occupied by 1 analog channel. These signals are all RF, just different types of modulation - much like 10M AM and FM - same frequency, same intrinsic information transmitted, but completely different modulation schemes.

-Jim