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This lesson talks about maintenance of no service and no 4G, 5G signal

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No service actually means that the mobile phone cannot make calls

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There is no call signal on the mobile phone, we usually call it no service

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No 4G No 5G means that the mobile phone can make calls,

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but does not display the logo of 4G or 5G signal

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Mainly from the following five aspects

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First, the radio frequency concept of the mobile phone and the composition of the radio frequency circuit

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Second, the sequence of repairing the four major circuits without service

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Third, the failure phenomenon and reason of no service, how the frequency band is divided and used

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Fourth, maintenance methods about no service

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Fifth, the maintenance method of making calls but without 4G or 5G network

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First look at radio communication

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Mobile phone calls and surfing the Internet rely on wireless electromagnetic waves

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to transmit information in space

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What is radio communication?

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Radio communication is to modulate the electrical signals such as sound and text data and images

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that need to be transmitted on wireless electromagnetic waves,

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and transmit them to the other party through space or ground

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This communication method is called radio communication

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It uses wireless electromagnetic waves to transmit information in space,

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mainly relying on wireless electromagnetic waves

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To sum up, mobile phone calls and surfing the Internet mainly rely on a kind of radio communication technology,

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and radio communication mainly relies on the transmission of wireless electromagnetic waves

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For example, in the picture, this is mobile phone 1 and this is mobile phone 2

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When making a call, the signal of mobile phone 1 will become electromagnetic waves,

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which will be transmitted to the base station through electromagnetic waves in the air,

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and the base station will send it to another base station after processing

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Another base station will transmit a signal to mobile phone 2

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This completes a transmission of a mobile phone signal

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The signal of mobile phone 2 is sent out and turned into electromagnetic waves,

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which are received by the base station,

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processed by the base station and handed over to another base station

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Another base station transmits a signal to mobile phone 1, and mobile phone 1 processes the signal

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This completes the call process between mobile phones 1 and 2

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Mobile phone calls or surfing the Internet rely on electromagnetic waves in the air

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This electromagnetic wave is a high-frequency electromagnetic wave

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The generation of electromagnetic waves is done by the antenna of the mobile phone,

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or by the antenna of the base station

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The antenna is a high frequency inductor

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Give it a certain high-frequency electrical signal, and it can become a high-frequency electromagnetic wave

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In the same way, the electromagnetic wave in the air is sensed by the antenna,

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and it will become a high-frequency electrical signal

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The voice, picture and video that the mobile phone wants are contained in this high-frequency electromagnetic wave

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The mobile phone just converts the high-frequency electromagnetic waves in the air into electrical signals,

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then performs a series of processing, and finally restores the sound, picture or video

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This high-frequency electromagnetic wave is generally processed by mobile phones at about 700 MHz to 5 gigahertz

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This is the frequency range of electromagnetic wave signals currently processed by mobile phones

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That's all for this lesson