I find that the transmission power of the rt2860 card in my netbook is limited to 6dBm. I believe this to be a driver problem. I would expect it to be able to handle 15dBm, but I cannot easily test this due to my present location and having temporarily swapped the card for an Intel 3945 card. (The chip is an rt2872.)
I suspect you are being limited by regulatory enforcement code. Please attach the output of dmesg shortly after booting and establishing a wireless connection.
Created attachment 27079 [details] dmesg output (regdom=EU) Kernel log attached. However, I don't see how regulatory enforcement code explains how all is well with the card swapped out for an Intel 3945 card...
"EU" isn't a valid regulatory domain, and hasn't been for some time. Judging from your email address, I would suggest "GB" as an alternative. With the (non-existant) "EU" setting, you are defaulting to the "world" regulatory enforcement. This limits you to 6dB. In the case of the Intel device, it specifies a default regulatory domain based upon values in its EEPROM instead. I suspect that setting an appropriate regulatory domain will resolve this, so I'm going to close it preemptively.
Looks like making that change has fixed things, though iwconfig is still reporting 6dBm and attempting to set the tx power to 15dBm causes an "invalid argument" error.
I'm not sure why you would still be limited to 6dBm, but it is possible I misread the regulatory database. The output of dmesg would be helpful for determining the cause.
Looks like the problem is either a dummy net/wireless/db.txt or a lack of Debian packages for wireless-regdb and crda... I've taken the quick way out: replace db.txt, recompile, re-install. After reboot, I have the following in the kernel log: cfg80211: Calling CRDA to update world regulatory domain cfg80211: World regulatory domain updated: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp) (2402000 KHz - 2472000 KHz @ 40000 KHz), (300 mBi, 2000 mBm) (2457000 KHz - 2482000 KHz @ 20000 KHz), (300 mBi, 2000 mBm) (2474000 KHz - 2494000 KHz @ 20000 KHz), (300 mBi, 2000 mBm) (5170000 KHz - 5250000 KHz @ 40000 KHz), (300 mBi, 2000 mBm) (5735000 KHz - 5835000 KHz @ 40000 KHz), (300 mBi, 2000 mBm) cfg80211: Calling CRDA for country: GB cfg80211: Regulatory domain changed to country: GB (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp) (2402000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm) (5170000 KHz - 5250000 KHz @ 40000 KHz), (N/A, 2000 mBm) (5250000 KHz - 5330000 KHz @ 40000 KHz), (N/A, 2000 mBm) (5490000 KHz - 5710000 KHz @ 40000 KHz), (N/A, 2700 mBm) Still showing 6dBm maximum, though.
The rt2800 code reads info from EEPROM regarding tx power. It would seem that your device has EEPROM info limiting it to 6dBm.
This is more or less known. rt2x00 reports incorrect txpower values to mac80211 on rt2800 devices and hence artificially lowers the used txpower in some cases. See [1] for more details. [1] http://rt2x00.serialmonkey.com/pipermail/users_rt2x00.serialmonkey.com/2010-June/001448.html