I’ve transmitted WSPR on 20M by toggling a Raspberry Pi GPIO pin thru a low pass filter, and had the signal spotted on WSPRnet at distances of over 2k miles. IIRC, that’s a transmit power of around 10 to 20 mW. A 6 dB attenuator would drop that down to 5 mW.
So would doing this on the 22M RFID segment be legal for unlicensed WSPR Tx? For, say, something like school student projects?