Part 2: Hardware modifications

The mCard-LoRa is a Mini-PCIe form factor card. Contains the common design of one SX1301 baseband and two SX1257 I/Q transceivers (1 TX and 2 RX) in a really small board.

The RF chain, highlighted in blue, has a balun, SAW filter, PA, filter and switch in the TX path and a SAW filter, LNA and SAW filter in the RX path. In the other layer there is a FTDI SPI to USB converter and some LDOs.

Mini-PCIe is the reduced version of PCI-Express with only one Express lane and adding USB and SIM card interfaces. There is a lot of only-USB Mini-PCIe cards and mCard can be one of them because we can see a pair of differential tracks routed between pins 36 and 38 to the FTDI chip.

Looking at power pins of the card, GND pins are routed to ground and 3.3v power pins (2, 24, 52) are routed the input of some voltaje regulators (the ones used for digital domain supply). But regulators inputs for analog domain are routed to pins 23 and 25. This doesn't meet the Mini-PCIe specification because that pins are assigned to the Express lane. The three LP38502SD-ADJ LDOs used for the analog part are adjusted to 3.3v output, then LDOs need a supply greather than 3.52v as the dropout is 220mV. In short, I decided to supply pins 23 and 25 of the Mini-PCIe connector with 5v from the USB connector. I have done this fix in the adapter bought at Aliexpress.

And that's all! No more hardware modifications are needed. I recommend you to use a good quality USB power supply. Raspberry-Pi 2 has USB current limiter that could prevent the concentrator to start up correctly, can be increased adding max_usb_current=1 to file /boot/config.txt

There are new MTAC-LORA2 boards that are compatible as well. But new MTAC-LORA-H and MTAC-LORA-SPI are not compatible, I will investigate them when I get such boards.

Internal photo taken from https://fccid.io/AU792U13A16856