Yeah...there's one called Leapfrog if that's what you're talking about. But, I'm not sure if that's really it because you call it a "modulator". It's not really a modulator, I'd call it a transmitter. You're basically transmitting the RCA (phono) signal through RF from TV to TV. So you don't actually need to point them at each other.

I believe Radioshack also sells these.