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mbar
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Joined: 19 Jan 2005
Posts: 1991
Location: Poland
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 Posted: Thu Jun 29, 2006 9:05 am Post subject: how to get 50 dBm with madwifi-ng? |
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| I use new atheros "turbo g" wireless card (PCI) in my gentoo router with madwifi-ng. A few times in madwifi documentation I could see in iwconfig output. Mine says only 18 dBm. How can I get higher transmit power? |
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Da Fox
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Joined: 06 Jul 2005
Posts: 342
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| Posted: Thu Jun 29, 2006 9:29 am Post subject: |
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I'm not sure, but I think it is possible that this is handled automatically, so in case the reception is bad (the card needs to resend a lot of packets) the output is increased?
I don't have any problems with the values, why would you want to increase it, are you experiencing poor reception? (If it ain't broken ...)
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"Man fears the darkness, and so he scrapes away at the edges of it with fire."
- Rei Ayanami
JGBE, a Java based GameBoy Emulator |
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mbar
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Joined: 19 Jan 2005
Posts: 1991
Location: Poland
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| Posted: Thu Jun 29, 2006 10:39 am Post subject: |
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| Yes, I experience poor reception in my home when I move my laptop two rooms from the router. |
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Da Fox
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Joined: 06 Jul 2005
Posts: 342
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| Posted: Fri Jun 30, 2006 12:14 am Post subject: |
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Well, you can set Tx-Power with 'iwconfig athX txpower nn': | Quote: | txpower
For cards supporting multiple transmit powers, sets the transmit
power in dBm. If W is the power in Watt, the power in dBm is P =
30 + 10.log(W). If the value is postfixed by mW, it will be
automatically converted to dBm.
In addition, on and off enable and disable the radio, and auto
and fixed enable and disable power control (if those features
are available).
Examples :
iwconfig eth0 txpower 15
iwconfig eth0 txpower 30mW
iwconfig eth0 txpower auto
iwconfig eth0 txpower off |
I don't know for sure if that will interfere with regular operations such as madwifi, but I think so. It's worth a shot 
_________________
"Man fears the darkness, and so he scrapes away at the edges of it with fire."
- Rei Ayanami
JGBE, a Java based GameBoy Emulator |
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mbar
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Joined: 19 Jan 2005
Posts: 1991
Location: Poland
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| Posted: Fri Jun 30, 2006 5:18 am Post subject: |
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| I tried that, anything higher than 18 dBm won't be accepted, yet I see people with 50 dBm. Kinda strange, are they violating radio regulations? |
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Da Fox
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| Posted: Fri Jun 30, 2006 11:35 am Post subject: |
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even if they where I don't think they'd care 
But this is odd, I know I could pump up my output all the way up to 50dbm not so long ago (well, perhaps that was with madwifi-pre-ng) but, now anything above 17dbm gives an invalid argument...
So something has changed, but I don't know what. Perhaps the cards never supported 50dbm and iwconfig only pretended for it to succeed? What are normal maximum levels for wireless cards?
_________________
"Man fears the darkness, and so he scrapes away at the edges of it with fire."
- Rei Ayanami
JGBE, a Java based GameBoy Emulator |
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mbar
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Joined: 19 Jan 2005
Posts: 1991
Location: Poland
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| Posted: Fri Jun 30, 2006 12:15 pm Post subject: |
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normal? dunno but here are legal levels for all countries:
http://www.nuclearcat.com/athmap.txt
e.g. for Poland:
| Code: | POLAND (PL, 0x268, 616) ETSI1_WORLD (0x37, 55)
2412G 18.0 2417G 18.0 2422G 18.0 2427G 18.0 2432G 18.0 2437G 18.0
2442G 18.0 2447G 18.0 2452G 18.0 2457G 18.0 2462G 18.0 2467G 18.0
2472G 18.0 5180A 16.0 5200A 16.0 5220A 16.0 5240A 16.0 5260A 16.0
5280A 16.0 5300A 16.0 5320A 16.0 5500A 17.0 5520A 17.0 5540A 17.0
5560A 17.0 5580A 17.0 5600A 17.0 5620A 17.0 5640A 17.0 5660A 17.0
5680A 17.0 5700A 17.0 |
It means the power for G revision is 18 dBm and for A revision 16-17 dBm depending on frequency. |
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widan
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Joined: 07 Jun 2005
Posts: 1512
Location: Paris, France
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| Posted: Fri Jun 30, 2006 8:19 pm Post subject: |
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| Da Fox wrote: | | Perhaps the cards never supported 50dbm and iwconfig only pretended for it to succeed? |
Probably. If you take the formula from the man page:
| Code: | | If W is the power in Watt, the power in dBm is P = 30 + 10.log(W) |
You also have the reverse formula:
| Code: | | W = 10^((P - 30) / 10) |
So 18 dBm is about 63 mW, which is reasonable for a wifi card. 50 dBm is 100 watts of RF power... Maybe a bit too much for a wifi card you can find inside a computer ! So it's unlikely the card is really outputting the indicated power (btw if you're interested in other powers, there is a dBm to W conversion table here). |
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mbar
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Joined: 19 Jan 2005
Posts: 1991
Location: Poland
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| Posted: Sat Jul 01, 2006 6:53 am Post subject: |
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Thanks for info!
But 18 dBm is reasonable only for latops with PCMCIA cards (IMHO) and I want to crank up tx power in my router, which has "stationary" Wifi PCI card. Polish radio regulations allow 100 mW of tx power, so this is 20 dBm. And I cannot set it with madwifi-ng also (it accepts nothing more than 18 dBm)... I know this card has 100 mW radio, as I can set it in Windoze. |
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