Weak current College】 【antenna works FAQ】.

<br> Keywords: aerial antenna classification bandwidth directional gain】 【summary antenna works FAQ <br> (1) antenna works and what is the role? A: the antenna as wireless communication is an indispensable part of its basic functionality is radiant and receive .radio waves. At launch, the high-frequency current is converted to electromagnetic waves; receive, stun nourishing wave converted to high-frequency current. (2) how many types of antenna? a: antenna varieties, mainly has following several kinds of classification .methods: by purpose can be divided into the base station antenna (base station antenna) and mobile station antenna (mobile portable antennas) press working frequency can be divided into long wave, long wave, wave, HF, UHF and microwave; by its orientation .can be divided into Omni and directional antennas; (3) how to select antenna? a: antenna as an important part of the communication system, the performance of direct impact communication system of indicators, users select antenna must focus on its performance. Specifically, .there are two aspects, first select the type of antenna; the second select antenna electrical properties. Select the type of antenna meaning is: the selected antenna pattern meets the system requirements of the radio wave overwrites; select antenna electrical performance requirements are: select antenna .frequency bandwidth, gain, rating, and other electrical indicators meets the system requirements. Therefore, when users select antenna is best to contact the manufacturer. (4) what is the gain of the antenna? a: gain is one of the key indicators of .the antenna, it is the direction of the coefficients and efficiency of product, is the antenna radiation or receive radio wave size. Gain size choice depends on system design to radio coverage of the requirements, to put it simply, equal, the higher the gain .of wave propagation in the distance, General base station antenna with high gain antenna, mobile station antenna has a low gain antenna. (5) what is the voltage standing wave ratio? a: input impedance of the antenna and feeder of the characteristic impedance of .inconsistencies, the resulting reflection and incident wave in feeder on the formation of magnetic waves superposition of the adjacent voltage maximum value and minimum value of a voltage standing wave ratio, it is the basis for the feeder transmission efficiency, VSWR less than 1.5 working frequency of .the voltage standing wave ratio less than 1.2, voltage standing wave ratio is too large, which will reduce the communication distance and reflex power returns transmitter power amplifier section that easily burned power amplifier tubes, impact communication system to work properly. Voltage standing wave ratio 1.0 .1.1 1.2 1.5 2.0 3.0 reflex power% 0 0.2 0.8 4.0 11.1 25.0 transmit power% 100 99.8 99.2 96 88.9 75.0 (6) what is the orientation of the antenna? a: antenna for space in different directions with different radiation or receiving capacity, this .is the orientation of the antenna. Measuring antenna directivity pattern is commonly used, in the horizontal plane, radiation and receive no direction antenna called Omni-directional antenna with one or more of the general direction of the antenna is called a directional antenna. Omnidirectional antenna .because of its non-directional, so most used in point-to-multipoint communication center. Directional antenna with a maximum radiation or receive directions, therefore energy concentrated, omnidirectional antenna gain relative to high, suitable for long distance point-to-point communication ., directional, and strong anti-interference ability. (7) how to understand the working frequency band width of antenna? a: antenna of electrical parameters are generally related to the operating frequency to ensure electrical parameters of indicators allowing the variation range of the frequency ., that is the work of the band width of antenna. General omnidirectional antenna of bandwidth to achieve operating frequency range of 3-5%, directional antennas work bandwidth to meet the operating frequency of 5-10%. (8) how to select the .cable and cable length? a: mobile communications systems often use characteristic impedance 50 Ohm coaxial cable as a feeder. In order to effectively put radio transmission to the antenna connector, you should minimize the feeder of transmission loss. Transmission loss depends on the diameter and .length of the cable, the same frequency, the greater the loss of cable diameter, the greater the loss of cable length, in principle, the requirements of cable transmission loss should not be more than 3 DB. The following table lists the common cable attenuation .(db / m), the user may act according to their own circumstances, a reasonable selection of cable types and length. Frequency model 150MHz 400MHz 900MHz SYV-50-7 0.121 0.203 0.295 CTC-50-7 0.060 0.100 0.165 CTC-50- .9 0.050 0.085 0.135 CTC-50-12 0.040 0.060 0.105 import 10D-FB 0.040 0.070 0.110 (9) how to select antenna installation location? answer: because of terrain and environmental impact, antenna receives electromagnetic waves is the direct wave scattering, reflection ripple .wave overlay, the results determined the receiving point amplitude and phase of field strength, and has a direct impact on the application of the antenna. Therefore, select antenna installation location should note the following aspects: 1, the transmitting or receiving antenna should avoid obstacles .(buildings, towers, bridges, etc.); 2, antenna site should try to keep away from sources of interference (high-voltage line, routes, Tower, roads, etc.); 3, the antenna should be mounted in a nearby .high ground: 4, if there are several pay antenna with a tower on work, special attention should be paid to the left and right between them and the spacing above and below in order to prevent mutual coupling affect system performance. (10) how to .install the antenna and cable systems? a: first antenna and feeder and parts requirements by product description, and then assembled at the antenna position, use fixtures fixed on pole antenna bracket, and the antenna and Tower of pole spacing is greater than the use of .parallel, reducing wavelength pole antenna performance. At antenna port Department, will feed wire connector (or cable) and antenna connected to bend a diameter of about 50 times in addition to complying with the diameter of the ring fixed on antenna bracket, Avoid connector parts .directly affected by the force and breakage or damage. (11) the antenna and cable system how to waterproof? a: antenna and feeder lines mainly depend on the connector, use self-adhesive rubber sealing tape, stretching back to half on the form wound .in succession, you can play a good waterproof seal. In addition, the feed lines into the rooms at the bend of a return to bend, to avoid the rain along the feed line into interior equipment. (12) how to detect the antenna and .cable systems? a: after erection of the antenna and cable systems should be professional and technical personnel to use a dedicated testing instruments for testing. Usually in the transmitter and the antenna and cable systems between threaded through-type power meter, test equipment transmitter power .and lighting power to judge system is working. <br>.