I tried to reproduce your issue. I am able to establish a connection between two gen 2 boards. They are approximately 15 meters away and the time of response increases as the boards get further away from each other as expected. However I am only able to test this in a lab so I’m not really sure how this would behave on an outdoor environment. I also tried to increase the tx power of the antenna using the same command as you did. Trying to increase the txpower gave no results because the value didn’t change when typing iwconfig wlan0, but when trying to decrease that value with iwconfig wlan0 txpower 10 I am able to change the Tx-Power to 10. So it seems that the Tx-Power is by default at its max. I guess this is because of security reasons and that this “Tx-Power=15 dBm” is the max tx power that should be used with this board to avoid malfunctioning. Some of the issues that might occur when increasing the tx above the default are overheating, more data errors and voltage drops that might lead to reboots.
Thank you for your tests. I indeed think that the transmit power is limited by the WIFI card, especially for power saving purposes, on mobile devices. I will probably need to connect my board to a WIFI router (plugged on 220V) to increase the range of my signal.