This article explains how I use a surplus Blonder-Tongue agile modulator as an in-home TV transmitter:
http://www.antiqueradio.org/HomeTVTransmitter.htm
You plug in your source -- anything that provides standard audio/video signal -- and it transmits on one channel at a time, using an old set of rabbit ears or a more elaborate antenna if you like.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html