While it's an interesting theory, there are a few things to think about.

The broadcast stations are still broadcasting. ET will still detect a signal, I mean it wasn't as if they would be able to decode what they were seeing. There's still a signal going out, but it's just begins at a different frequency.

In fact, with the advent of satellite communications, there are even more signals being sent out today than even 5 years ago.

Beside TV stations, AM and FM stations continue to transmit signals, as do shortwave radio stations.