Looks like you already debugged it - you're likely seeing interference between the two radios, and will need to plan on an installation with sufficient antenna separation to avoid the problem. Using xr9's, the problem would be much worse; we plan on a minimum antenna separation of 15 feet when doing dual-radio 900 Mhz installations. The lower the frequency, the greater the required physical separation.
Tom S.
----- Original Message -----
From: LAMBA Jaideep
To: madwifi-devel@lists.sourceforge.net
Sent: Thursday, November 19, 2009 11:33 AM
Subject: [Madwifi-devel] XR2 and XR5 performance difference

I have two XR2 radios close to each other on one PCI board. With this setup I am seeing a throughout of 30 Mbps combined from two radios (which should be around 60Mbps). If I switch the radios with XR5 I start seeing 60 Mbps throughput.

XR2 + XR2 + antennas == 30 Mbps (should be around 60 Mbps)
XR5 + XR5 + antennas == 60 Mbps
XR2 + XR2 + cable on radio pair == 60 Mbps.

Can somebody please suggest some pointers to debug this problem with two XR2. 
I am using trunk madwifi (r4022) and the interfaces are configured for adhoc mode with minstrel rate control algorithm. I suspect interference.
Any suggestions are welcome.

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