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This lesson talks about the circuits and components related to no service fault

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The picture shows the line of the general mobile phone call channel

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Let's first look at the main role of these components in the circuit

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RX is receive, TX is transmit

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When receiving, the antenna turns electromagnetic waves into electrical signals,

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which is the role of the antenna when receiving

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When transmitting, the antenna converts the high-frequency electrical signal of the mobile phone

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into electromagnetic waves

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This is what the antenna does

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The coaxial switch is used for factory testing

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In fact, its two pins are connected by a wire

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These two pins can be shorted during maintenance

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Usually here is pin 1, here is pin 2,

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and the other two pins are ground wires

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The filter is to filter out clutter, for example, the signal sent by the antenna may have many different frequencies

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For example, from TV stations and radio stations, these signals will also be sensed

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The filter will filter out some clutter and transmit the signal of the frequency band required by the mobile phone

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The antenna switch is also divided into receiving and transmitting

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When receiving, it switches the signal from the antenna to the receiving channel

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When transmitting, it switches the high-frequency signal to the antenna end and transmits it

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Its function can be understood as switching the reception and transmission of each frequency band

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so that reception and transmission do not interfere with each other

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This is what the antenna switch does

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Some small antenna switches switch the signal of the antenna,

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not just the signal of a certain frequency band

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The codes of the antenna switch in the drawings are: W or SW or ASM

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Next we look at the receiving amplifier in the receiving channel

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The receiving amplifier amplifies the signal switched by the antenna switch

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Because the electromagnetic wave signal is very weak after it becomes an electrical signal

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The English name of the receiving amplifier in the drawing is called LNA

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The power amplifier is to amplify the transmission

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The high-frequency signal from the radio frequency is very weak

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It needs to be amplified by the power amplifier and sent to the antenna before the base station can receive it

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If power amplification is not performed, the base station cannot receive the transmitted signal

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It is usually called PA, PAM or PAD in drawings

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The role of RF transceivers

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The high-frequency signal received by the antenna contains the voice of our speech

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We can regard the high-frequency signal as a carrier

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The RF transceiver removes the carrier, that is, strips out the voice signal,

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and turns the high-frequency signal into a low-frequency signal, which is generally a kilohertz signal

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The signal is given to the baseband through the IQ bus, and the baseband thoroughly demodulates it

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When receiving, the baseband demodulates the signal, finally restores the sound,

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and sends it to the CPU through the I2S bus

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When transmitting, the baseband CPU modulates the sound signal to form a low-frequency sound signal

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This low frequency signal cannot be transmitted over long distances

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The RF IC mixes the low-frequency signal to carry the voice signal to the high-frequency electrical signal

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High frequency transmit signals are generated by radio frequency transceivers

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We can simply understand that the function of the radio frequency transceiver is to

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generate high frequency when transmitting,

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and carry the low frequency voice to the high frequency signal

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This high-frequency signal has been formed, and after power amplification,

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it is finally transmitted to the antenna switch.

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High-frequency electrical signals become electromagnetic waves and are received by the base station

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This is the role of the main components of the radio frequency circuit

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RF IC has its own power supply, power amplifier chip also has power supply,

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receiving amplifier and antenna switch also have power supply

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Filters and coaxial switches are not powered

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The failure of these elements appearing in the figure will result in no service

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That's all for this lesson