[yosito]

It wasn't like the Soviets could just turn their TVs to the right channel. I doubt the Soviets knew what frequency they were using, and analog video is still "encoded" in the radio waves. These signals still required that specialized $300,000 equipment (which I'm sure was top secret at the time) to make sense of.

[slededit]

The height of the antenna would give away the frequency. But the soviets had good spy penetration into the US industrial base so it's likely they already knew anyways.