I've got CPE Wifi router and i want to upgrade its LTE module

Dear Community,

i know nothing about OpenWrt and coding (programming etc) but let me share my goal:

i've got a huge number of WiFi routers (1000+ pcs) supporting FDD LTE Band 7 only (2600Mhz) and 3G 1900 Mhz (it is absolutely useless). I want to upgrade the device in order to make it work with 3G 2100 Mhz and 4G 1800 and 2600Mhz accordingly. For this purpose i can use a donor: ZTE MF823 USB modem. And my question is: how can i combine these 2 different devices? My technical assistant says he can apply MF823 motherboard to WiFi router but we still need OpenWrt coder to write the software.

If your routers can run OpenWrt and have a USB port, it would be a matter of installing OpenWrt and the modem drivers on the router. The original 3G modem inside the router could be removed. You would use the new ZTE USB modem as a unit without modifying it.

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It doesn't have USB port.
I removed an original GSM module and replaced it with another module supporting all bands and it worked (but this new module is crazy expensive so i need to find an economical solution).
So if it doesn't have USB port i can't install OpenWrt software?

The suggestion, as I understood it, was that if it did have USB, then you could possibly save the effort of tearing apart the "donor" USB-enabled units and just plug them in to the USB port.

You should be able to install OpenWrt if/when the device is supported without needing USB.

Jeff, got the point, thank you!
How do i know if the device is supporting OpenWrt?

Are you certain that a software upgrade will enable other bands on this device?

https://openwrt.org/toh/start

not sure, here is the photo of original GSM module (QDC - with limited bands) and Asus module with all bands working: module
We didn't do anything apart of replacing the modules. Once Asus module inserted all bands were open and worked.

But Asus-like module is very expensive, the cheapest one i found is $30/pc. So i want to use ZTE MF823 motherboard as GSM module.

We opened the modules and it's different, so i don't think the software could add more bands (QDC is left one): qdc%20vs%20vodafone

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Here is the device: Quanta QDC. This is similar to Asus 4G-N12

The firmware that runs in the modem itself is always closed-source.

And as you found, the first modem only has one RF section, for 1900/2600. The other one (naturally more expensive) has another power amplifier chip and set of filters to cover other bands.

Technically a miniPCIe cellular modem links to its host by USB. Though it is a PCIe form factor, the PCI bus pins are unused. The plug only supplies power and USB to it.

This means you could make a hardware adaptation to connect a regular USB-A device to the router via the USB pins in the PCIe slot.

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@mk24 covered alot...but I want to be more clear...radios tend to be hardware-based (not software-based), because that requires a Variable Frequency Oscillator (VFO) $.

It's highly uncommon for such devices to be "unlockable" to other bands in digital applications (usually for regulatory purposes).

EDIT: Don't play with radio equipment in FCC-US Land (other countries are worse) if you aren't sure. Study for Amateur Radio or something...better than a fine or an investigation...

E.G. ...I don't assume you're in the US...it could be illegal in your nation to carry data on certain cellular bands...or they could be allocated for data-only to a certain carrier, etc.

You need to know this.