What do you mean by effective scanning frequency band? What do you mean by effective scanning frequency band?

About the meaning of effective scanning frequency band, the explanation of computer technical terms and terms

It is divided into horizontal scanning frequency (line frequency) and vertical scanning frequency (field frequency). Horizontal scanning frequency: the movement of electrons from left to right on the screen is called horizontal scanning, also called line scanning. The number of scans per second is called the horizontal scanning frequency, and the horizontal scanning frequency of the video projector is fixed, which is 15.625KHz(PAL system) or 15.725KHz(NTSC system). The scanning frequencies of data and graphics projectors are not in different frequency bands. In this frequency band, the projector can automatically track the line frequency of the input signal, and the phase-locked circuit realizes complete synchronization with the line frequency of the input signal. Horizontal scanning frequency is an important index to distinguish the level of projector. A projector with a frequency range of 15kHz-60kHz is usually called a data projector. Those whose upper frequency exceeds 60kHz are usually called graphic projectors. Vertical scanning frequency: the electron beam moves from top to bottom during horizontal scanning. This process is called vertical scanning. Each scan forms an image, and the number of scans per second is called vertical scanning frequency, also known as refresh frequency, which indicates the number of times to refresh the image per second. The vertical scanning frequency is generally not less than 50Hz, otherwise the image will flicker.