Noise Figure Noise figure is a measure of how much noise is added to the signal by passing it through the tuner. All tuners add noise. For some applications like analog TV, there is no clearly defined boundary on how much noise can be added. Other applications, especially in digital ones like cable modems and set-top boxes, there are very clearly defined boundaries of how much noise can be added by the tuner. Distortion Distortion is a measure of how much the tuner distorts or changes the incoming signal.
All tuners distort the signal to some degree.
Image Rejection All tuners have the undesired effect of tuning to the desired channel as well as to an image channel. To eliminate this image channel, tuners employ special filters and circuitry. Image rejection is especially important in systems such as cable systems where every channel is used. It will also be highly important in the reception of terrestrially broadcast digital television. The transition from analog to digital broadcasting is having a profound effect on tuners.