I have found the TiVo actually requires a better quality signal than your average STB.

I don't know if it is due to the signal being split into the two tuners, or if the tuners themselves are not that sensitive/selective.

In my case I could not use the TiVo HD in place of a working (no Dropouts) STB. But by adding an amp the TiVo HD is fine.

This may not work for you if you are getting more noise than signal at your location.

Peter.