A digital TV amplifier is a device intended to boost the signal received by a television from over-the-air broadcasts, also known as the terrestrial signal. Most commonly the aim is to deal with problems caused by a weak signal leading to interference or even missing channels. Occasionally this type of device may be used if an aerial is shared by multiple channels in a home.
In principle, a digital TV amplifier is needed for the same reasons that an analog TV amplifier is required: that the home is in a position where a roof-top aerial cannot get a strong enough reception from the local transmitter for the TV to display a complete picture without interference. In practice, homes that were able to survive without an amplifier for analog TV may still need one for digital broadcasts. This is because a TV working from a weak analog signal can usually still display a picture, albeit one with distortion or "snow" on the screen. With digital television there is a much quicker drop-off from a good picture to one with "blocky" interference and then to having no reception of a channel whatsoever.
To complicate matters, digital television broadcast channels in batches, sometimes known as a mux, with each channel in a batch sharing the same frequency. Depending on the location and the nearby transmitter, the TV may not receive all batches at the same strength. This could mean, for example, that the TV picks up a perfect signal for 24 channels, has serious interference on six channels, and cannot pick up another six channels altogether. TV owners therefore need to check all listed channels to be certain whether they could benefit from a digital TV amplifier.
The most common form of amplifier is one that sits between the aerial cable coming into a property and the TV set. Better results may be possible by attaching an amplifier directly to the base of the aerial itself, though this requires roof access and usually involves professional installation. These amplifiers shouldn't be confused with a TV distribution amplifier. This works in the same way as a standard indoor digital TV amplifier, but is intended to make up for the loss of strength when the signal from an aerial is split between multiple TV sets. It may not provide enough amplification if the homeowner both has multiple TV sets and a poor aerial reception.
Though less common, it is possible for the signal to a television to be too strong rather than too weak. This can cause problems with digital television, particularly if a strong signal for one batch of channels "crowds out" a weaker signal for another batch. The solution in this case is not a digital TV amplifier, but rather an attenuator. Although using slightly different methods, it is effectively a reverse amplifier and will reduce the strength of a signal.