Thanks for your help, all, especially Reyk, Sevan, Fred, Joakim.
Here is some more information.
My card is a NETGEAR Wireless PCI Adapter 32-bit WG311T
and I use my box as an AP.
Reyk, I patched my sys with your file.
I have this message:
/bsd: ath0: bogus xmit rate 0x0 (idx 0x3)
Sevan advised me to use "media autoselect"
He was right, it works and the 11M is applied by default.
To remind you, I did force the DS11
> cat /etc/hostname.ath0
inet 192.168.1.1 255.255.255.0 NONE media DS11 chan 8 nwid SPEENICS
mediaopt hostap
Thanks Sevan and sorry for annoying the list.
On the other hand, I can't use OFDM54 and use the 802.11g feature.
Well, it's not a problem for me, but I can perform tests for you, Reyk,
if you need.
Bye.