Reach frequency for communication with the microwave (microwave) is 300-3000 MHz (called ultra-high frequency, abbreviated UHF) and 3000 30000 MHz (called super-high frequency, abbreviated SHF). “UHF frequencies up called microwaves, though there is also a limit of 1000 MHz. The frequency is typically used by companies around the listrik’adalah frequency (band) 400 MHz, 2000 MHz and 7000 MHz.
Specification of equipment used for radio communications at a frequency of about 400 MHz is shown in Table 6-6. The emission wavelength is limited to the distance that can be seen, namely for communications between stations by multiplex communication circuit below 24 channels (CH). Lately, the system is widely used for car radio communication for the maintenance of power lines around the city (suburb). How it works closely with VHF communications.
Telecommunications with microwaves used for communication channels that require the most important channel to talk a lot. In such case, the cost for each channel pernbangilhan talk dibandingkandengan most inexpensive method of communication. Another advantage is that the noise of a little, good voice quality and high reliability.
Compared with the PLC communication, microwave communication cheaper, because the price of the capacitor hook and line traps on expensive PLC communication. Except that, for PLC equipment needed large gains because of the noisy voltage corona, especially at very high voltages. Therefore, when a speech channel enarn or more, microwave communication is more economical and more stable.
Microwaves emitted by a straight line (such as light). Therefore, the microwave emission is limited to direct wave beam within the distance that can be seen (except beam scattered waves in the troposphere). This means, that the beam loss (propagation loss) between the emission point and the receiving point changes depending on the refraction in the air (which is a function of the temperature in the soil, air pressure, humidity, geographical position) as well as the influence of the reflected wave (reflected). These fluctuations are called symptoms disappear (fading). The further the distance beam of radio waves and the higher the frequency, the greater the disappearance of symptoms.
In pernbangunan series of microwave, radio stations must be put in place where the symptoms disappear not be much going on. The circuit should also be planned taking into account the loss-beam because the symptoms disappear earlier. As a microwave antenna used electro-magnetic lens, reflector antenna horn or parabolic antenna. Due to economic considerations antenna latter is widely used by power companies. Each of these antennas can be adjusted (matched) with kearahan (directivity) that thorough and acquisition of power (power gain) high. Characteristics of microwave telecommunication is made possible by the quality of this antenna. As shown in Figure 6-91 parabolic antennas (parabolic antenna) consists of a parabolic reflector and a primary radiator that radiates waves to the reflector.
As a conduit (feeder line) is usually used coaxial cable for the frequency of about 2000 MHz, while guiding-wave (wave guide) square, elliptical or round used for frequencies around 7000 MHz. As shown in Figure 5-93 to enable the wave reflection in a certain direction to use a flat metal reflector reflector called passively. This reflector is usually a 3 mx 4 m, 4 m or 6 mx 6 mx 8 m.
Microwave telecommunications equipment consists of a transmitter and a radio receiver, air repeater (repeater) and tool-carrier frequency. Today all this equipment already ditransistorkan. The best example of a solid-state repeater (solid state) shown in Figure 5-90. Aircraft repeater relay system typically uses detective (detective relay system) that receives gelornbang micro, mendemodulasikannya, took part video and then radiates it back after memodulasikannya again. There is also a heterodin system, which amplifies the received micro wave after changing into a VHF frequency, and then radiates it back after changing its frequency into the microwave. This latter system is rarely used by power companies.
