Có 11+ tài liệu thuộc chủ đề "hệ thống sóng RF"
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Hertz demonstrated radio frequency (RF) generation, propagation, and reception in the laboratory. Marconi's wireless communications using the telegraph meant that a ship was no longer isolated in the open seas and could have continuous contact to report its positions. In the early 1900s, most wireless transmission occurred at very long wavelengths.. In the 1920s, the one-way broadcast was made to...
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At low RF, a wire or a line on a printed circuit board can be used to connect two electronic components. They can be classi®ed into two categories: conventional and integrated circuits. They can be used for wired communications to connect a transmitter to a receiver (Cable TV is an example).. FIGURE 2.2 The currrent distribution within a wire operating...
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The antenna is a key component in any wireless system, as shown in Fig. FIGURE 3.1 Typical wireless system.. FIGURE 3.2 Various antennas [2].. If the source transmitting power is P t , the power density P d in watts per square meters at a distance R from the source can be calculated by. At a distance far from the...
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Various Components and Their System Parameters. Figure 4.1 shows a brief history of microwave technologies. These components can be represented by the symbols shown in Fig.. FIGURE 4.1 History of microwave techniques: (a) technology advancements. FIGURE 4.2 Symbols for various components.. A directional coupler is a four-port device with the property that a wave incident in port 1 couples power...
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The input signal to the receiver is in the frequency range of 20–470 MHz. Other receiver examples are shown in Fig. Most components shown in Figs. This chapter will discuss the system parameters of the receiver.. The performance of the receiver depends on the system design, circuit design, and working environment. For the output signal to be useful, the signal...
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Figure 6.1 shows a typical transmitter block diagram. The output signal could be upconverted to a higher frequency.. The power amplifiers are used to increase the output power before it is transmitted by an antenna. To have a low phase noise, the oscillator or local oscillator can be phase locked to a low-frequency crystal oscillator. Power output and operating frequency:...
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The nature of an echo signal provides information about the target—range, direction, and velocity.. Although radar cannot reorganize the color of the object and resolve the detailed features of the target like the human eye, it can see through darkness, fog and rain, and over a much longer range. It can also measure the range, direction, and velocity of the...
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Three such satellites can provide services covering all major population centers in the world. Wireless personal and cellular communications have enjoyed the fastest growth rate in the telecommunications industry. The received power is P r and the distance is R. The received power can be calculated in the following if we assume that there is no atmospheric loss, polarization mismatch,...
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The lower frequency is called the modulating signal, the higher frequency signal is called the carrier, and the output signal is called the modulated signal. The benefits of the modulation process are many, such as enabling communication systems to transmit many baseband channels simultaneously at different carrier frequencies without their interfering with each other. Some simple modulation can be achieved...
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Multiple-Access Techniques. 10.1 INTRODUCTION. Three commonly used techniques for accommodating multiple users in wireless communications are frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Frequency division multiple access and TDMA are old technologies and have been used for quite a while. Code division multiple access is the emerging technology for many new...
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11.1 RADIO NAVIGATION AND GLOBAL POSITIONING SYSTEMS Radio navigation is a method of determining position by measuring the travel time of an electromagnetic (EM) wave as it moves from transmitter to receiver. 11.1 and 11.2.. Figure 11.1 shows an example of an active radio navigation system. Several typical radio navigation systems are shown in Table 11.1 for comparison. FIGURE 11.1...