It turned out that Mi Note LTE (Dual Sim) support LTE B3 and B7 (The international version supports B1 and B3)
But my carrier Vodafone UK rolled out LTE throughout the courtry with band 20 (800Mhz) but LTE Band 7 is only available for 3 cities at the moment. ( Only EE and Three support B3/B7, which is the reason I cannot see 'Vodafone 4G' and 'O2 4G' but 'EE 4G' and 'Three 4G' in the network list. source, source, source)
So I tried the guides: here, here, here and here to unlock B20 on my phone. (Many thank to @BlackSoulxxx, @fffft, @olokos, @devilsshadow and @Albirew)
I went through all the steps and set the value into 6828 (and even 6829) permanently but still cannot see 'Vodafone UK 4G' or 'O2 UK 4G' on the network list.
I googled a lot but still couldn't find the solution.
I found others who have Xiaomi Mi Note or Redmi have the same problem and want to unlock different LTE bands. But some of them stuck in the middle of the steps especially the prerequisites and couldn't go through. Maybe unlocking other LTE bands is working for them. So I decided to write the step by step guide and hopefully throw out a brick to attract a jade.
The lawyers made us do it.
We have to post an obligatory warning.
We don't think that this mod will cause you any problems. But we can't guarantee that. I never tried it on devices other than Mi Note LTE (dual sim).
You assume all risks if you proceed, including the risk that your phone might object, meltdown, brick or void your warranty.
1. Root your device.
2. enable diag mode by entering *#*#717717#*#* on the dialer and download the driver from here (thank @m11kkaa).
Once diag mode enabled, you can see the Device Manager from PC like this:
then right click the first 'MI NOTE LTE' and install the driver you just downloaded
you will see this if successful
3. Download and install QPST
4. Download and install QXDM
5. Open the "QPST Configuration" program, you should see below straightaway:
You couldn't see this until you finished step 2 successfully
6. Now select the QPST Start Clients > Software download > Backup > Start. Wait until the status says 'memory backup completed'. This saves a backup copy of your phone's stock NV memory to your computer in case you need it later.
7. Leave QPST open and navigate to the C:\Program Files (x86)\Qualcomm\QXDM\Bin folder. And right click on QXDM.exe > run as administrator.
8. Go to options -> communications
Target port -> select COM6, then OK
9. select Nv Browser from view
10. select LTE from Category Filter, then you can see 06828 and 06829
11. click on line 06828 (lte_bc_config); click the Read button, save somewhere the original value in case something goes wrong (inside notepad or anything), the original value on my device is 2061584302148
12. Let's talk more about the value, source
in my case, the value for 06828 is 2061584302148, using Calculator (programmer mode) to change it to binary value is
from right to left, the 3rd, 7th, 38, 39, 40,41 bit are 1, which means band 3/7/38/39/40/41 are enabled
I want to enable band 20 so change the 20th bit to 1
the corresponding Dec value is 2061584826436
13. click on line 06828 (lte_bc_config); click the Read button, replace Input value with 2061584826436 (please don't be an idiot and don't edit the empty one with "ext" in the name) and click on Write button
OK THAT IS IT. Restarted Mi Note, and then see if the value set permanently.
BUT LTE BAND 20 IS STILL NOT UNLOCKED.
I changed the value to 2061584826368 which is
Disable B3 and B7 to see if the value is working, It worked, I cannot see EE 4G and Three 4G any more.
let me know if anyone unlocks other bands
ps: don't forget to disable diag mode by entering *#*#717717#*#* on the dialer.
DID I MISS ANYTHING?!
and thanks in advance for any idea.
Thanks @BlackSoulxxx, @fffft, @olokos, @devilsshadow,
@Albirew and @m11kkaa anyway even if I couldn't unlock Mi Note, I had a lot fun playing it.