Featured Articles
Announcing Pi
Technical Specifications
Raspberry Pi FAQs
Win a Pi
Raspberry Pi Wishlist
Actions
Forum Thread Details
  • Replies 27 replies
  • Subscribers 669 subscribers
  • Views 6483 views
  • Users 0 members are here
Related

RT3070 wireless adapter adjust tx power??

wallarug

I seem to be unable to adjust the tx power above 20dbm.  I have tried: 'iwconfig wlan0 txpower 22' but this does not change the txpower.

 

I have also disabled the power-management.

 

The adapter claims that it can hit 5800mW of power which aquates to about 37dBm.

 

Does anyone know how I can get the txpower up? (I can put it down, just not up)

 

root@raspberrypi:~# lsusb

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.

Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.

Bus 001 Device 004: ID 148f:3070 Ralink Technology, Corp. RT2870/RT3070 Wireless Adapter

root@raspberrypi:~# iwconfig wlan0 txpower 30

Error for wireless request "Set Tx Power" (8B26) :

    SET failed on device wlan0 ; Invalid argument.

root@raspberrypi:~#

Parents

  • In practice the wifi adapter is unlikely to support such a high output (5800mW would require more than 1A at

    5V USB supply) (is this a normal USB stick type of wifi adapter?). 20dBm is more likely though. A a bit odd why it claims 5800mW specifically. Maybe they meant 580mW (which is still really huge for wifi).

Reply

  • In practice the wifi adapter is unlikely to support such a high output (5800mW would require more than 1A at

    5V USB supply) (is this a normal USB stick type of wifi adapter?). 20dBm is more likely though. A a bit odd why it claims 5800mW specifically. Maybe they meant 580mW (which is still really huge for wifi).

Children
  • in reply to shabaz

    Here is the link to the product:

    http://www.ebay.com/itm/KINAMAX-High-Power-5800mW-802-11b-g-n-150Mbps-Wi-Fi-Wireless-Network-Adapter-/150904547616?ssPageName=ADME:X:RTQ:US:1123

     

    I know that this is on ebay but I did my background research and every website said 5800mW with 58dBm antenna.

  • in reply to wallarug

    It sounds like they are relying on a directional antenna which makes sense (no need to radiate a huge power everywhere). So, they are possibly implementing 20dBm output with a 17dBi antenna (this would be extremely directional). It looks like there are antenna topologies for 17dBi for such frequencies, e.g. this one.

  • in reply to shabaz

    Going on what you said before:

    In practice the wifi adapter is unlikely to support such a high output (5800mW would require more than 1A at

    5V USB supply) (is this a normal USB stick type of wifi adapter?). 20dBm is more likely though.

    I think you are somewhat right.

     

    Maybe Linux limits the amount of Watts (current in this case) that you can pull out of the USB port.

     

    I did a quick google search:

    http://en.wikipedia.org/wiki/DBm

     

    Have a look at the table halfway down the page:

    dBm levelPowerNotes
    80 dBm100 kWTypical transmission power of FM radio station with 50-kilometre (31 mi) range
    62 dBm1.5 kW = 1,500 WMaximum legal power output of a U.S. ham radio station.[3]
    60 dBm1 kW = 1,000 WTypical combined radiated RF power of microwave oven elements
    50 dBm100 WTypical thermal radiation emitted by a human body

    Typical maximum output RF power from a ham radio HF transceiver

    40 dBm10 WTypical PLC (Power Line Carrier) transmit power
    37 dBm5 WTypical maximum output RF power from a handheld ham radio VHF/UHF transceiver
    36 dBm4 WTypical maximum output power for a Citizens' band radio station (27 MHz) in many countries
    33 dBm2 WMaximum output from a UMTS/3G mobile phone (Power class 1 mobiles)

    Maximum output from a GSM850/900 mobile phone

    30 dBm1 W = 1,000 mWTypical RF leakage from a microwave oven

    DCS or GSM 1,800/1,900 MHz mobile phone. EIRP IEEE 802.11a (20 MHz-wide channels) in either 5 GHz Subband 2 (5,470–5,725 MHz) provided that transmitters are also IEEE 802.11h-compliant, or U-NII-3 (5,725–5,825 MHz). The former is EU only, the latter is US only.

    29 dBm794 mW
    28 dBm631 mW
    27 dBm500 mWTypical cellular phone transmission power

    Maximum output from a UMTS/3G mobile phone (Power class 2 mobiles)

    26 dBm400 mW
    25 dBm316 mW
    24 dBm251 mWMaximum output from a UMTS/3G mobile phone (Power class 3 mobiles)

    1,880–1,900 MHz DECT (250 mW per 1,728 kHz channel). EIRP for Wireless LAN IEEE 802.11a (20 MHz-wide channels) in either the 5 GHz Subband 1 (5,180–5,320 MHz) or U-NII-2 & -W ranges (5,250–5,350 MHz & 5,470–5,725 MHz respectively). The former is EU only, the latter is US only.

    23 dBm200 mWEIRP for IEEE 802.11n Wireless LAN 40 MHz-wide (5 mW/MHz) channels in 5 GHz subband 4 (5,735–5,835 MHz, US only) or 5 GHz subband 2 (5,470–5,725 MHz, EU only). Also applies to 20 MHz-wide (10 mW/MHz) IEEE 802.11a Wireless LAN in 5 GHz Subband 1 (5,180–5,320 MHz) if also IEEE 802.11h compliant (otherwise only 3 mW/MHz → 60 mW when unable to dynamically adjust transmission power, and only 1.5 mW/MHz → 30 mW when a transmitter also cannot dynamically select frequency).
    22 dBm158 mW
    21 dBm125 mWMaximum output from a UMTS/3G mobile phone (Power class 4 mobiles)
    20 dBm100 mWEIRP for IEEE 802.11b/g Wireless LAN 20 MHz-wide channels in the 2.4 GHz ISM band (5 mW/MHz).

    Bluetooth Class 1 radio. Maximum output power from unlicensed AM transmitter per U.S. Federal Communications Commission (FCC) rules 15.219.[4]

    19 dBm79 mW

     

    This would give three reasons as to why I can't put more than 20dBm into the device:

    1) It is sort of illegal

    2) The maximum normal output of wireless devices is normally only 100mW (20dBm)

    3) You cannot draw 5.8Watts out of a USB port on the raspberry pi (I think 5volt * 500mW = 2.5W would be the maximum before you need a powered hub or blow it up)