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This lesson talks about the allocation of 2G frequency bands

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No service means that the frequency band of the mobile phone is out of order,

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that is, the 2G frequency band is out of order

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No service means no signal strength bar on the phone

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If the mobile phone displays the E network, it is the 2G network of China Mobile or China Unicom,

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and the display of 1X means that it is the 2G network of China Telecom

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It no longer shows the signal strength bar when the 2G channel has problems

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2 g channel actually contains receive channel and transmit channel

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In addition, it should be noted that

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whether the radio frequency circuit is in the calling frequency band or 4G, 5G,

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it is a path channel of the signal that is composed of components that the frequency band passes through

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Whether it is a phone call or a circuit for 4G and 5G Internet access,

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they are all based on frequency bands in the drawings

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Find which components the frequency band passes through in the line

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If there is an abnormality in the channel, the call cannot be made,

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or the call can be made but the Internet cannot be accessed.

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To understand the 2G frequency band here, you must first know the three major operators

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The three major operators in China are China Mobile, China Unicom and China Telecom

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The frequency bands of China Mobile and China Unicom are usually called GSM frequency bands

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GSM has four frequency bands

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GSM 850, GSM 900 are called low frequency bands,

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and will be referred to as GSM_LB, G_LB, or 2G_LB in the drawings

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GSM 1,800 and GSM 1,900 are called high frequency bands, referred to by GSM HB or G_HB, 2G_HB

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Among them, the reception of GSM 900 and GSM850 frequency bands go through the same channel,

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but their transmission does not go through the same channel

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These are GSM900 and GSM 1,800 receptions

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Some mobile phones have their own separate receiving channel, usually referred to by DCS

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If there is no separate DCS code, GSM 1,800 reception, you have to find B3 reception

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It takes the same channel as the reception of the B3 frequency band

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The transmission of GSM 1,800MHz does not take the same channel as B3,

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it has its own separate transmission channel

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Generally, GSM transmissions have TX and RX

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TX is transmit, RX is receive

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China Telecom's 2G frequency band is called BC 0 in some drawings,

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and it is usually used to refer to earlier models

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Most of the current mobile phones use the B26 frequency band,

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and there are generally these three codes in the drawings

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This is the allocation of the 2G band

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That's all for this lesson