Common sense knowledge about wireless signals

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Common sense knowledge about wireless signals [Copy link]

What is a signal and where is there a signal? Usually when we use our mobile phones, we often say that the signal is poor and the mobile phone has no signal. There are signals everywhere in life. Mobile phone signals are "radio waves" and "radio signals". They are invisible and intangible. Today we will talk about the knowledge about signals. Figure 1 Poor signal, difficult to talk Radio signals can usually be detected by oscilloscopes, spectrum analyzers and other equipment. Radio signals can be described by parameters such as frequency, amplitude, and phase. For general maintenance personnel, the phase of the signal is rarely concerned. 1. Frequency of the signal Frequency refers to the number of periodic changes in a signal per unit time. The international unit of frequency is Hertz (Hz). Simply put, if a signal changes periodically only once in 1 second, the frequency of the signal is 1Hz; if a signal changes periodically only twice in 1 second, the frequency of the signal is 2Hz, as shown in Figure 2. There are many radio signals, and frequency is equivalent to the name of the radio signal. Different radio signals can be distinguished, detected, identified, and separated by frequency, and different signals, circuits, and wireless applications can also be distinguished. Figure 2 Schematic diagram of 1Hz and 2Hz signals Hertz (Hz) is the basic unit of frequency. In practical applications, there are also kilohertz (kHz), megahertz (MHz), gigahertz (GHz), etc. Their conversion relationships are as follows: 1000Hz = 1kHz 1000kHz = 1MHz 1000MHz = 1GHz 2. Signal amplitude Amplitude refers to the maximum rise and fall values of the signal waveform. It indicates the strength of the signal and is usually expressed in voltage (V). In the signal waveform diagram shown in Figure 3, the number of changes of signal A and signal B per unit time is the same: that is, the frequencies of signal A and signal B are the same. But the amplitude of signal A is larger than that of signal B. Figure 3 Schematic diagram of analog signal amplitude 3. Signal gain and loss After a signal passes through an electronic component or circuit, its strength (amplitude) will change. If the output signal of a device or a circuit is larger than the input signal, then it exhibits "gain", as shown in Figure 4. We call this device or circuit an amplifier or an amplifying circuit. Figure 4 Gain diagram If the output signal of a device or a circuit is smaller than the input signal, then it exhibits "loss", as shown in Figure 5, which can be called experiencing attenuation or being attenuated. Figure 5 Loss diagram Understanding signals is the basis of consolidating electronic knowledge. We have just explained the mobile phone signal. In the future, if the mobile phone signal is poor, we can know the reason.