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This lesson goes on to talk about the transmission channel of Huawei P40 B3 frequency band

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As we said in the last class, the transmitting signal reaches the 25th pin of the power amplifier U4701

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After it is amplified, it outputs to the next chip through pin 25,

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and the next chip is usually the antenna switch.

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We open the drawing

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The transmitting signal of B3 leads to the 12-pin of U4701, and it is output from the 25-pin after internal power amplification

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We search for it

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The transmission signal of B3 passes through the circuit formed by the capacitance and inductance

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After frequency selection, it continues to go, and the name becomes MH_FEMID signal

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We check where it goes next

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It leads to pin 8 of the chip U4801

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This chip is called the antenna switch of the medium and high frequency band.

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Why is it an antenna switch?

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Because the following characteristics can be known

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Both receive and transmit signals are connected here

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Second, it has nomenclature defined as the antenna signal connected to the antenna terminal called ANT

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We got here according to receive and transmit, and this chip it has ANT pin

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Then this chip must be an antenna switch or contain an antenna switch, but it does not contain a power amplifier

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The transmitting power amplifier has a separate chip outside

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Then it's just the antenna switch

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The transmission signal of B3 is sent to the eighth pin of the antenna switch

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Then this antenna switch is to turn on the eight-pin transmit signal under control conditions.

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Who does it connect to? The eight pins are connected to the 38-pin or 39-pin antenna

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In fact, it has two channels. Let's see which channel it is.

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38 and 39 belong to the high frequency band HB

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MB is the mid-band antenna

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The B3 frequency band belongs to the middle frequency band,

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and the transmission signal of the middle frequency band has the path of the antenna of the middle frequency band

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After the transmitted signal is amplified, it reaches pin 8 of the antenna switch

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Pin 8 and 36 of the switch are connected

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After that, it goes here

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After passing the components, it reaches the six pins of the filter Z4801

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For this filter, the transmit signal enters from pin 6 and exits from pin 2

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Get here, it's called MHB_CA

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It reaches the first pin of the double pole four throw switch U5601

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leads to the three pins, it connects from here to the antenna direction

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It passes through the first pin of the filter.

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After the filter filters out the clutter, the third leg outputs

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Eventually it leads to this antenna J5607

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This is the transmission signal of B3

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The antenna is installed on the antenna base

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The antenna will turn this high-frequency electrical signal into electromagnetic waves and send it into the air, and the base station will receive it.

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That's all for this lesson