ral, rum and bi-antenna

Sam Leffler sam at freebsd.org
Tue Aug 5 16:05:15 UTC 2008

David Naylor wrote:
> Hi,
> I happen to have the good fortune of owning a RT2661S (ral driver) and a 
> RT2601USB (rum driver) [manufactured by Canyon].  Both chipsets have the 
> ability to handle two antenna.  
> Now the good fortune, both chipsets default to the wrong antenna.  When I 
> should be getting a stable connection at about -70dBm instead I am getting 
> very poor connection (less than 50% connectivity, reported from ping) and 
> about -90dBm.  
> After looking at the FreeBSD driver code (and the [Open/Net]BSD) the antenna 
> selection is marked as *TBD*.  Does anyone know how to add antenna selection 
> (the ralink linux drivers are a wild maze).  I considered trying to do it 
> myself but I do not know the first thing about kernel hacking (let alone 
> chipset drivers) and have no idea where to start.  
> I was thinking a stop-gap solution will be to have the antenna selectable 
> using tunables/sysctl?  
> Needless to say I am very willing to try any patches (and even attempt to 
> create one myself if someone could point me in the right direction...).  

So far as I know the hardware provides no help in this area; e.g. like 
switching antenna ports on retry attempts or reporting which antenna was 
used to tx/rx a frame.  I don't even know if the h/w does rx diversity.  
I believe the ralink drivers for these chips do some form of s/w 
diversity or antenna switching.

Otherwise you can certainly hookup a sysctl to fix the antenna; ath has 
code to do this you can crib.  At some point we'll get around to hooking 
up ifconfig (I've delayed as MIMO makes this api slightly more involved 
then pick one of auto, 0, 1).

But the bigger question is why you're seeing such a difference when 
locking tx to one port or another; it sounds like the antenna design on 
your card is highly directional.  This is not unexpected for USB devices 
where every penny is scrimped in design+manufacture but cardbus cards 
typically are better.  Cardbus cards often have U.FL connectors under 
the sheath so if you're willing to canibalize your card you can remove 
the sheath and attach good antennae to see if you get better behaviour.

> Regards
> David
> P.S. Anyone know the release schedule for 6.4 and 7.1?

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