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This lesson talks about the sending and receiving channels

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of the mobile 4G B40 frequency band of Xiaomi mobile phones

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This circuit describes the specific receiving and transmitting channels

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of Xiaomi's mobile 4G frequency band,

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that is, if the circuit in this channel fails, it will cause the Xiaomi mobile phone

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to plug in the mobile card to make calls but without 4G

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Let's take a look together, first look at the reception

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Its receiving channel is from this J0204 which is the antenna

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Here is the representative antenna, in fact it is an antenna holder

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The received signal from the antenna pedestal arrives at this coaxial switch

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The two pins of the coaxial are conducting

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It transmits this received signal over

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Of course, this antenna converts high-frequency electromagnetic waves

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into electrical signals and transmits them.

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For example, the 40 frequency band, it receives the signal and comes from here

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After coming over, the clutter is filtered out by the filter, it comes in from the third pin, and the fifth pin outputs

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Receive the signal and keep going until you reach a double pole double throw switch

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Double pole double throw switch can also be called small antenna switch

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The eight-pin and six-pin of this switch can be turned on,

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and the received signal is transmitted after the switch is turned on.

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It's just a switch

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The receiving signal of this B40 frequency band continues to go

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Then this foot is named as the antenna signal of the high and medium frequency bands

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It goes to this amp plus antenna switch

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At this time, the reception reaches the power amplifier, it does not perform power amplification,

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it just reaches the internal antenna switch

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Switch the receiving signal to pin 9 to form a specific frequency band signal

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For example, the B40 frequency band, it comes out from the 9th pin

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B40 PRX is the main receiver, that is, the receiver of the B40 frequency band

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This received signal reaches the U1001 receiving amplifier

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Because the incoming signal is very weak, it only needs the antenna

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to convert it into an electrical signal on the way

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Receive the power amplifier to amplify the power of the signal, and output it from F4 pin after amplification

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Then it goes to the V15 pin of the RF transceiver

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The frequency of this B40 band is relatively high, more than 2,000 megahertz

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It cannot be used directly connected to the speaker, nor can it directly display pictures and other things

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The signal is sent to the RF chip, and the RF chip performs mixing

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After mixing, pass it to the baseband U1601 through the q link bus

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The baseband demodulates the signal and sends it to the CPU through the Pcie bus

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This is the line that receives

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Let's see the launch

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The transmission is that the information of the mobile phone is transmitted to the baseband through PC IE,

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and the baseband is modulated

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After modulation, it is sent to the RF chip through the UL bus of Qlink

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The RF chip performs up-conversion, and then generates a high-frequency carrier,

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carrying these pictures and video information, and outputs them to the 20-pin of the power amplifier.

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After internal power amplification, go out from pin 57

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It should be noted here that it is named ANT, that is, both reception and transmission go from here

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It walks to S0307

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The six-pin and eight-pin conduction of the double-pole double-throw switch

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After the conduction, the unnecessary clutter is filtered out by the filter,

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and then the conduction of the normally closed contact finally reaches the antenna

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The antenna turns this high-frequency electrical signal into a high-frequency electromagnetic wave

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and sends it into the air, and the base station receives it

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This is the principle of the sending and receiving channel of the mobile 4G B40 frequency band of Mi 10 Pro

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That's all for this lesson