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This lesson talks about the receiving and transmitting channels of the GSM 900 of Huawei mobile phones

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Take Huawei's Mate 30 5G version as an example

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Open the schematic diagram and bitmap of Huawei Mate 305G version

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Search for the antenna's codename ANT in the schematic

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We can find that ANT_LB_MAIN is the main antenna of the low frequency band,

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because GSM 900 belongs to the low frequency band

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But this location is not the description of the antenna, I double click it

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On page 46 of the drawing, you can see a low-band main antenna, J5703

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This seat is actually an antenna seat

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Let's look at the reception of the G S M 900

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The electromagnetic wave in the air is sensed by the antenna buckled in the seat J5703,

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and the antenna turns it into an electrical signal

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This high-frequency electrical signal wants to go forward

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The inductance at this end grounded is frequency-selective,

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we can ignore it and only look at the inductance on the series channel

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The signal is coupled through this capacitor, and after frequency selection by the inductance, it reaches the RF1 pin of the chip U5704

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This component is called double pole dual system switch, DPDT, also called small antenna switch

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Its control pin is controlled according to the high and low level

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When the control pin is low, RF1 and RF 3 are turned on, and RF 2 and RF 4 are turned on

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When the control pin is high level, RF 1 and RF 4 are turned on, and RF 2 and RF 3 are turned on

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The antenna signal enters from the RF1 pin and exits from the RF3 pin

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Why is it like this?

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The RF2 and RF4 conduction time will be longer, because the RF2 pin belongs to the diversity receiving antenna, also called the discontinuous receiving antenna

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it comes from this location

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But this position comes from the fact that other antenna ends are turned on after passing through this normally closed contact

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This is diversity reception, our maintenance priority is to look at the main set reception, that is, the antenna of the RF1 pin

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RF1 and RF3 conduction

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Although the name here is LB_PRX, the main set receives, but this antenna signal also includes transmission, we first look at the reception

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The received signal is coupled by capacitive coupling, and then frequency-selected by inductance

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There is a symbol at the position of the inductance, which means cancellation

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The received signal reaches the three pins of the filter Z5701

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In from 3 feet, out from 1 foot

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When firing, it enters from pin 1 and exits from pin 3

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Let's double click on it to see where it leads

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This is not what we are looking for

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It got to this position

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This asterisk means that the component does not exist

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Since it does not exist, the receiving signal will not work here, so we don't care about it

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The signal reaches pin 31 of the chip U4901 after frequency selection by the inductor

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ANT_L is the antenna signal of the low frequency band

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We will see that it forms the transmission signal of each frequency band,

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including the reception signal, B8, B12, B20 frequency band, B26-B28 frequency band

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This chip is a low-band antenna switch, because it is connected to the low-band

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This is the wiring from GSM900 to low band antenna switch

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That's all for this lesson