"WDino"
** It is actually far better than that. Analogue TV signals cannot operate on adjacent frequencies - there has to be a wide vacant gap equal to another channel between any two stations. ( Chs 9 and 10 are separated by ch 9A - which is to be used for digital ) So for the usual 4 analogue channels to co-exist requires that another 7 or 8 channels be left vacant - one above and one below each channel.It is by the elimination of these vacant blocks of spectrum ( about 50 MHz worth in each capitol) that new services will be made possible.
It is even better with the UHF band - with digital services all 41 channels can be occupied in the same area instead of the previous max of about 20.
So, allowing 3 x SD signals per channel number results in a possible 123 digital TV channels on UHF !!!
Another benefit is how much closer stations using the same frequency can be located - with analogue there has to be hundreds of miles of separation as even the slightest signal from a distant same frequency transmitter produces a visible image on the screen. With digital, the significantly stronger signal wins out and no sign of the weaker one is seen.
............. Phil