Gizmo said..
Every channel that appears on your TV, radio etc has its own transmitter, that converts the incoming signal from the studio to an RF signal (Radio Frequency).
The towers that are around often have many antennas on them, often radio, TV stations, taxi companies, Telco's and lots of other businesses will lease space on a single tower to mount their communication equipment.
Well, that's not quite accurate with digital TV. Each 'channel' can be part of a multiplexed stream on a transponder. Maybe the terms are different between terrestrial TV and satellite, but DVB over satellite uses a transponder that is broken up into different streams.
In theory, in an area that does not justify multiple transmitters you could run a number of competing channels, i.e. 7,9, and 10 over the same frequency.
