The difference between sync level and black level in analog TV standards is about 15% of maximum transmitter power. This means that any noise added that is more

The difference between sync level and black level in analog TV standards is about 15% of maximum transmitter power. This means that any noise added that is more than 7.5% of max power will confuse the TV to detect sync as black and black as sync. In practice, a 20dB SNR or less will be completely unwatchable. The Shannon limit for a 5Mhz channel with 20 dB SNR is 17 Mbit/s and latest DTV standards approach this, easily 10, maybe 15 Mbit. That's enough for a HD channel in perfect quality or many more in SD. So the problem is not with analog vs digital, that debate is long settled. It's the specific tradeoffs made when digital TV was deployed.