[qldbureau]

Good evening,

To excuse, if my question is stupid…

On the PCB, I see a site (place) for a module TX-RF.

There are no silly questions 

The AQI is designed so that it can simply work by itself and not send data anywhere other than its LCD screen.
It can be setup to display on the LCD if one wants to, and transmit data to a Rx2 Plus receiver; and into the future.
With transmission there is no need for LCD, but is a personal choice.

From testing versions, the transmitter was setup to work alongside Tx 1, so set to the same ID as Tx 1 in the receiver. The AQI is a physical transmitter in its own right.
If this is different now, Werk or another of the development and testing team will correct 

Hope this helps in the meantime.