As an indispensable part of wireless communication, the basic function of antenna is to radiate and receive radio waves. The function is to convert the electromagnetic wave from the television station into signal voltage to the high frequency .
The way a TV antenna works is that when an electromagnetic wave moves forward, it hits a metal antenna, it cuts a magnetic field line, and it creates an electromotive force, which is the signal voltage.
As an important part of the communication system, the performance of the antenna directly affects the index of the communication system. The user must pay attention to its performance first when choosing the antenna.
One of the main indicators of an antenna is the gain, which is the product of the directional coefficient and the efficiency, and is the expression of the size of the antenna radiation or received waves.The choice of the gain size depends on the requirements of the system design for the radio wave coverage area. Simply put, under the same conditions, the higher the gain, the farther the radio wave propagation distance. Generally, the base station antenna adopts the high gain antenna, and the mobile station antenna adopts the low gain antenna.
TV receiving antenna is generally line antenna (satellite receiving antenna is surface antenna), according to the frequency range of the received high-frequency signal can be divided into VHF antenna, UHF antenna and all-channel antenna; According to the frequency band width of the receiving antenna, it is divided into single-channel antenna and frequency antenna. According to its structure, it can be divided into guide antenna, ring antenna, fishbone antenna, log periodic antenna and so on.
The open-circuit TV program received by the cable TV system mainly includes two frequency bands: ⅵ (channel 1-4) and ⅷ (channel 6-12) in VHF band and UIV(channel 13-24) and UV(channel 25-48) in UHF band. In VHF frequency band, the special channel antenna that receives TV signal of a specific channel is generally selected, and the best receiving position is selected for installation, so that it has the advantages of high gain, good selectivity and strong directionality. However, the partial-band antenna used in ⅵ and ⅷ and the all-channel antenna used in VHF have wide frequency band and low gain, which are only suitable for some small systems. In UHF frequency band, a pair of frequency band antennas can generally receive television programs of several channels which are closely separated.
Post time: Aug-25-2022