The broadcasting station transmits programming from their studio to the high power broadcasting towers generally located near most major urban areas. These towers then rebroadcast the signal to the homes and houses nearby where the signal can be picked up by the TV antenna in your home.
At Mohu we work with improving the TV antenna in your home to allow you to receive stations more clearly and from further away.
Digital TV is actually capable of a higher resolution than cable or satellite, but some broadcasters choose to use a lower resolution which allows them to transmit multiple programs (or streams) in the same bandwidth, which is called multi-casting. As a result you may be able to receive multiple channels from NBC or FOX, for example.
It is important to note that based on location and other factors, not everyone is able to receive free TV.