Lyngemark Satellite Charts Sat. The following addresses the differences in the video standards of television broadcasting.
Television receivers require a source of field timing reference signals, or field rates .
These signals tell the television receiver to be ready to receive the next picture in the stream of images. Early television sets used the Mains power supply frequency as this source. There are two good reasons. The first is that with the older types of power supply, you would get rolling hum bars on the television picture if the Mains supply and power source were not at exactly the same frequency. The second is that television studios would have had enormous problems with flicker on their cameras when making programs.