TVGuardian must sit between the source (a tuner) and your TV to be able to read the closed-captions and intercept the audio before you hear it. You can use TVGuardian with over the air TV, however, you need an external ATSC tuner or a Tivo DVR. For standard definition TVs, you will need a DTV converter box.
The LT works very similar to our previous units in that it requires a yellow composite video connection for the Closed Captioning. In order for the LT unit to work with Antenna TV or Coaxial connections, you will need an external tuner, a cable/satellite box or converter of some sort, or an old VCR; then connect the VCR to TVGuardian LT using the composite video cable (the VCR would need to be turned on when watching TV). TVGuardian will also only work with 1 TV at a time.
Here are some links to explore. We have not been able to test the products in the links, but they should work with TVG.
http://www.tivo.com/
http://www.firebird-systems.com/graphics/dct210/digital-tv-tuner-hdmi-dct210.shtml