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Afaik;

For mobile broadband 4G/3G, low frequency gives better wall penetration. For 4G, only TM Unifi Mobile has been allocated the low frequency Band 5 = 850MHz. For 3G, only Maxis has been allocated the low frequency Band 8 = 900MHz. Unfortunately, Unifi Mobile has poor 4G Band 5  coverage and 3G Band 8 is limited to maximum 7.2Mbps.

Most of the other 4G/3G frequencies allocated to the mobile telcos are high frequency Bands of above 2000MHz = not-good for wall penetration, eg 4G Band 7 and Band 38 = 2600MHz, 3G Band 1 = 2100MHz.

So, the problem of wall penetration is not with the phone but the frequencies allocated to the mobile telcos by the government.

TM Unifi Mobile has no 3G network of its own because of very late entry into the market = it rides on Celcom's 3G and 4G networks for limited data, ie unlimited data for Unifi Mobile phone plans is only for its own 4G network, not on Celcom's 3G/4G network = unlimited data only if covered by Unifi Mobile 4G network.

UMobile was also a late entry to the market = its 3G network coverage is poor but its 4G network coverage is OK and getting better = it used to ride on Maxis's 3G network.
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LTE band 20
secret band used by YES 4G LTE, umobile, digi, maxis 

When I put my U Mobile in oppo and vivo phones within price range RM1,299 and below ( 4G band 1, 3, 5, 7, 8, 38, 40 and 41 ), the signal in my house has dropped to 3G, very unstable and totally cannot online.

When I put it in SAMSUNG, HUAWEI / HONOR and Xiaomi Redmi phones ( 4G band 1, 3, 5, 7, 8, 20, 28, 38, 39, 40 and 41 ), the signal in my house is 4G, good and stable.

It's just my own experience only. Nothing to do with fan or not fan.

So means with 5g the coverage would get better?

When I put my U Mobile in oppo and vivo phones within price range RM1,299 and below ( 4G band 1, 3, 5, 7, 8, 38, 40 and 41 ), the signal in my house has dropped to 3G, very unstable and totally cannot online.

When I put it in SAMSUNG, HUAWEI / HONOR and Xiaomi Redmi phones ( 4G band 1, 3, 5, 7, 8, 20, 28, 38, 39, 40 and 41 ), the signal in my house is 4G, good and stable.

It's just my own experience only. Nothing to do with fan or not fan.

LTE band 20
secret band used by YES 4G LTE, umobile, digi, maxis 

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Afaik;

UMobile uses only 4G LTE Band 7 = 2600MHz and 3G Band 1 = 2100MHz.  So, the problem should lie with the lower quality 4G modem inside the mid-end Oppo and Vivo phones, eg can only detect strong 4G signal = at least 3 bars.
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LTE band 20
secret band used by YES 4G LTE, umobile, digi, maxis 

U mobile are you mabuk?

U mobile are you mabuk?

U mobile are you mabuk?

Where do you get the info that Umobile, digi, and maxis are able to use band 20 for LTE?

Digi and MAXIS not sure, but U Mobile and YES are using 4G band 20.

When I put my U Mobile in the oppo or vivo phone without this band in my room ( as I mentioned before ), 4G become H, just 1 bar only and totally cannot online.

After that, I put it in the phone with band 20 in the same place, the line straight away go back to 4G, almost full bar most of the time and can online.

If it is not this problem, can you explain what is the reason?

Digi and MAXIS not sure, but U Mobile and YES are using 4G band 20.

When I put my U Mobile in the oppo or vivo phone without this band in my room ( as I mentioned before ), 4G become H, just 1 bar only and totally cannot online.

After that, I put it in the phone with band 20 in the same place, the line straight away go back to 4G, almost full bar most of the time and can online.

If it is not this problem, can you explain what is the reason?

When I put my U Mobile in oppo and vivo phones within price range RM1,299 and below ( 4G band 1, 3, 5, 7, 8, 38, 40 and 41 ), the signal in my house has dropped to 3G, very unstable and totally cannot online.

When I put it in SAMSUNG, HUAWEI / HONOR and Xiaomi Redmi phones ( 4G band 1, 3, 5, 7, 8, 20, 28, 38, 39, 40 and 41 ), the signal in my house is 4G, good and stable.

It's just my own experience only. Nothing to do with fan or not fan.

Digi and MAXIS not sure, but U Mobile and YES are using 4G band 20.

When I put my U Mobile in the oppo or vivo phone without this band in my room ( as I mentioned before ), 4G become H, just 1 bar only and totally cannot online.

After that, I put it in the phone with band 20 in the same place, the line straight away go back to 4G, almost full bar most of the time and can online.

If it is not this problem, can you explain what is the reason?

Frequencies used on U Mobile Network in Malaysia Frequency

Frequency .............................................Width..........Protocol ........Notes
900 MHz (900~905, 945~950)..........  2 * 5 MHz ... HSPA+ 
1800 MHz (1730~1745, 1825~1840)  2 * 15 MHz  LTE 
2100 MHz (1920~1935, 2110~2125)  2 * 15 MHz  HSPA+/LTE  2x10MHz LTE in some area
2600 MHz (2520~2530, 2640~2650)  2 * 10 MHz  LTE 

4G LTE frequency bands in China

China uses mainly TDD LTE in various bands for the 4G service. China Mobile uses three spectrum bands of 1.9 GHz, 2.3 GHz and 2.5 GHz for 4G LTE service, which are respectively Band 39, 40 and 41. Similarly, China Unicom uses 1800 MHz, 2.3 GHz, and 2.5 GHz, namely band 3, band 40 and band 41. Among them, only band 3 (1800 MHz) is the FDD LTE. Lastly, China Telecom uses 1800 MHz, 2.3 GHz, and 2.5 GHz the same as that of China Unicom. But China Telecom will add 2.1 GHz and 850 MHz frequency band to increase the speed significantly using Carrier aggregation.

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https://en.wikipedia.org/wiki/U_Mobile
https://en.wikipedia.org/wiki/LTE_frequency_bands

https://www.soyacincau.com/2017/05/24/u-mob...5g-in-malaysia/ - U Mobile is the first to launch 4.5G in Malaysia - By Alexander Wong 10:52 am, 24 May 2017
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For 4G LTE, UMobile first used only Band 7 = 2600MHz nationwide in the early 2010s, and then gradually added Band 3 = 1800MHz and sporadic Band 1 = 2100MHz from 2017 onward, ie likely gradually in major city areas only.

LTE Band 20 is specific to Europe only.
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Well it might not be true. Band 20 is used by YTL Yes too.

https://www.malaysiainternet.my/2019/11/ytl-yes4g-800mhz/

Networks on LTE band 20 (LTE-FDD) are suitable for roaming in ITU Region 1 only.

Anyone knows what this mean?
seems like among the 4 major telco.. UM is the lowest allocation...

Frequencies used on Maxis network in Malaysia Frequency 

Frequency ................................................. width ........... Protocol  .......Notes
900 MHz (905~915,950~960) ................ 2 * 10 MHz .. GSM/HSPA+/LTE 
1800 MHz (1710~1730, 1805~1825) ..... 2 * 20 MHz .. GSM/LTE ..... 2x20MHz LTE (mostly)
..................................................................................................................2x15MHz LTE in some area

2100 MHz (1935~1950, 2125~2140)......2 * 15 MHz .. UMTS/HSPA+/LTE
2100 MHz.................................................. 5 MHz (TDD band) ..............2x5MHz/2x10MHz/2x15MHz on LTE

2600 MHz (2510~2520, 2630~2640) .... 2 * 10 MHz .. LTE 
2600 MHz (2500~2510, 2620~2630) .... 2 * 10 MHz .. LTE ................ Spectrum sharing with Redtone