Expert ~ Transmit power settings

Important: Except for low-power Ralink dongles (see below), there is no need to increase transmit power! If you have range problems, check your wiring, power supply, antennas etc. and make sure you are on a free channel.

• Alfa AWUS036NHA: Card is set near maximum power, another 1-2db could be gained, but at the expense of wider signal shoulders and uncleaner signal

• Alfa 051/052NH: Card is set to maximum power, do not increase, you will get badblocks if you do.

• TPlink 722N (and other low-power AR9271 dongles): Card is set to maximum power, no need to increase.

• CSL 300Mbit stick (and other low-power Ralink dongles): Increase txpower to +4 for maximum output.

• Ubiquiti WifiStation USB: For these cards, transmit power needs to be decreased. Maximum txpower setting is not yet known, probably somewhere between 46 and 54. Start with 46 to be on the safe side.

Setting transmit power

• Login to the linux console (see here on how to do that)

Atheros:

• Type e.g. txpower_atheros 50 to change txpower value to "50". Min. value is 1, max. value is 63, default is 58.

Ralink:

• Type e.g. txpower_ralink -2 to change txpower value to "-2". Min. value is -5, max. value is 5, default is 0.

After setting transmit power, type reboot to restart and apply settings or poweroff if you want to powerdown the Pi.

Determining the maximum transmit power settings for yet unknown wifi dongles

• First, make sure wiring and power supply is good, if not, you will get problems and badblocks
• Start with a low value, -2 for Ralink and 36 for Atheros
• Find a free channel. This is important. On 2.4Ghz, finding a free channel can be next to impossible. In that case, you can 'simulate' a free channel by removing the antennas on the GroundPi and keeping the AirPi right next to the GroundPi
• Test if everything works correctly. Let it run for some minutes, you should see near zero packetloss.
• Increase transmit power, then rinse and repeat until you find the spot where further increasing transmit power leads to the packetloss counter steadily increasing
• Decrease transmit power again until you see no more packetloss and then decrease it a little more to be on the safe side
• Test again. Let it run for an hour, you should see almost zero packetloss. Also check for heat, if the dongles get too hot, they will either reduce transmit power or produce packetloss.