Analogue sets will not work once the signal is turned off by 2012
About 500,000 households across the South will have to re-tune their televisions as part of the digital switchover due in 2012.
Freeview, BT Vision or Top Up TV viewers in Hampshire, Isle of Wight, east Dorset and West Sussex will need to re-tune their equipment.
Channel Five is also switching off its analogue signal serving Gosport, Isle of Wight, Southampton and Portsmouth.
The channel can still be watched on digital TV.
Digital UK said the changes were required as part of a reorganisation of airwaves ahead of the region's switch to digital TV due to take place in 2012.
Satellite and cable television is unaffected by the changes.
David Scott, chief executive of Digital UK, said: "Making these changes now is vital to protecting existing services from interference and ensuring that the process runs smoothly in three years' time.
"Analogue viewers who make the switch to digital now will be able not only to continue enjoying Five but also many extra TV channels, radio and text services.
"For digital viewers, retuning their equipment should only take a few moments and we are here to offer advice to anyone who needs it."