Adjusting TX Power & EIRP

Why change it?
This is a very important step if you want to operate the system legally. By default the DroneBridge system might have a too high EIRP depending on your setup and location.
The output power might be too low (not enough range) or too high (lost packets and max. EIRP)
If you are using an un-patched Kernel/drivers and don't go crazy on the antennas you should be on the save side EIRP wise, but your hardware might not operate at the "range sweet spot".
From the hardware section you can get an idea about the max possible power output of some WiFi adapters. If you do not know what EIRP is go read up on it! It depends on the TX power of your card and dB rating of your antenna. There is a max rating for it depending on the band (2.4 GHz/5.x GHz) you want to use. Because DroneBridge is a digital system the max EIRP for DroneBridge in the EU is ​
100 mW (20 dBm) - 1, 2, 5.5 and 11 Mbps, CCK modulation, 2.4 GHz band
63 mW (18 dBm) - g/n-Rates, OFDM modulation, 2.4 GHz
100 mW - 1000 mW (30 dBm) - 5.x Ghz
As you can see the case is a little more complicated with the 5 GHz rage. Some cards in monitor mode might support DFS and TPC while others don't.
General rules are:
Stick to the ISM bands
High power cards might need lower settings. Low power cards might need higher settings
Stay away (~1km+) from others that might be affected by the extensive use of your set frequency
Data rates of nearby WiFi networks are heavily affected by DroneBridge and vise versa
Good antennas have a much higher effect on range than output power
Too high power settings can damage your hardware, result in packet-loss and can lead to less range because the hardware is operated outside its sweet spot.
How to change?
You can measure the TX power of your card using a power meter. As for now there is now there is no general way of adjusting the power output. Depending on your chipset you need to change the following parameter:
Atheros (AR9271)
In general there is no need to further increase the TX power as the hardware already operates at its max by default.
The the Ubiquiti Wifistation EXT you may need to lower the power to stop packetloss.
To change (set via driver parameter): 
Go to the console and type  txpower_atheros xx where xx is a value from: 1-63 with 50 being the default value
Reboot
Ralink
To change (set via driver parameter): 
Go to the console and type txpower_ralink xx where xx is a value from -5 to 5 with 0 being the default value
Reboot
Realtek
Set via iw tx-power 30 inside the start script. Change value in line  pyw.txset(wifi_card, 'fixed', 3000) inside startup/init_wifi.py
Finding the right setting
Use an rf power meter to be sure about the actual power output & EIRP
Measure packet-loss inside shielded environment (basement or inside of micro oven might be just fine)
Start with low parameters and then increase

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Finding the right setting