Thousands of people who get their TV through an aerial need to retune their equipment, because the first stage of the Digital Switchover's taken place.
Freeview viewers in places like Bedfordshire, north Hertfordshire, Northamptonshire, Cambridgeshire and Milton Keynes are among those affected.
The first phase of the Digital Switchover at the Sandy Heath transmitter near Bedford saw analogue BBC2 signals switched off in the early hours of Wednesday 30 March 2011. The second phase - where analogue BBC1, ITV1, Channel 4 and Channel 5 will be switched off - is due to take place two weeks later, on Wednesday 13 April.
The retune required by Freeview, Top Up TV and BT Vision viewers on 30 March - and then again on 13 April - is because the position of the digital terrestrial channels will move at each Switchover phase. If you don't retune, you will start to lose channels.
The Digital Switchover means that if you haven't yet converted a TV to digital - whether it's your main set, or a secondary one in a kitchen or bedroom - you won't be able to pick up any channels from 13 April. TVs connected to a satellite or cable service, like Sky or Virgin Media, are unaffected by Switchover.
While 87% of households in the Anglia region have converted their main TV set to digital, only 67% have converted all their TVs. It's thought there are thousands of secondary TVs - in bedrooms and kitchens - that will have to be upgraded or replaced come the spring.
Peter Monteith from Digital UK said: "Every television set, if it's getting a signal from an aerial, whether it's on the roof or on top of the set, needs to be converted for digital. If you don't do anything and you're only watching analogue at the moment, which is just four or five channels, your screen will go blank."
Going digital means better picture and sound quality and more channels. By going digital, you will also be able to listen to Heart through your TV, as Heart broadcasts on Freeview (through an aerial) as well as Freesat and Sky (through a satellite dish).