The effective scanning frequency band is the general term of horizontal scanning frequency and vertical scanning frequency Horizontal scanning frequency: The movement of electrons from left to right on the screen is called horizontal scanning, also called scanning. The number of scans per second is called the horizontal scan frequency. The horizontal scan frequency of the video projector is fixed at 15.625 kHz (PAL system) or 15.725 kHz (NTSC system). In this band, the projector can automatically track the input signal line frequency. , By the phase-locked circuit to achieve full synchronization with the input signal line frequency. The horizontal scanning frequency is an important indicator to distinguish the projector grade. Projectors with a frequency range of 15 KHz to 60 KHz are often called data projectors, and upper limit frequencies of more than 60 KHz are often called graphic projectors. The horizontal scanning frequency of the projector has a range. If the horizontal scanning frequency of the input signal from the computer exceeds this range, the projector will not be able to project. Vertical scanning frequency: The electron beam moves from top to bottom while scanning horizontally. This process is called vertical scanning. Each scan creates an image, the number of scans per second is called the vertical scan frequency, and the vertical scan frequency is also called the refresh rate. It represents the number of times the image is refreshed per second, expressed in Hz, for example: 60 Hz or 60 times per second, the higher the frequency, the more stable the image. The vertical scanning frequency is generally not lower than 50Hz, otherwise the image will have a flickering effect. If the vertical scanning frequency of the input signal from the computer exceeds this range, the projector will not be able to project.