I'm sharing information how to get more rf power from china made rc522 board.
My project uses MFRC522 board and Mifare Ultralight C cards.
This board can not produce enough RF energy to get Ultralight C card up and running
MFRC522 datasheet says that max TX current is 150mA, but measured current was only 7mA.
I have a very good RF design experience so I started to measure whole RF part and make full tuning.
And what I found, antenna is tuned, not perfectly but usable, so was matching cirquit. But used 2.2uH
inductors does not meet with required parameters.
Solution: Replace inductors L1 and L2 with same inductance (2.2uH) but higher operating current.
like this one: http://www.tme.eu/en/details/cw1008-220 ... ferrocore/
Now RC522 can read Ultralight C cards with no problem, also NTAG203 card reading distance is ~70mmWARNING!!
RC522 RF output pins are very static sensitive!
Without proper equipment you can easly
damage your rc522 reader board!!