I had the same problem using both R52 and R52H cards. The SNR was realy low. And I found out the reason. This is awkward, but it's really happening. When the madwifi driver detect two antennas connectors on the R52 cards, it sets automatically the diversity up. Now, if you have two antennas physically connected to the card, this is fine. Nevertheless, I guess the most of you is using only one antenna connected to the MAIN connector. In this case you should take the diversity off and specify which connector to use to receive and transmit. You can check if you are using diversity in this way:
cat /proc/sys/dev/wifi0/diversity
PS: wifi0 or whatever is your wireless card.
If this command returns 1, it means that the diversity is enabled.
Furthermore:
cat /proc/sys/dev/wifi0/txantenna
If this returns 0, it means you are using transmission diversity.
The point is that you will definitely want to disable transmitter diversity if you only have one antenna connected. Otherwise 50% of your broadcast and multicast packets (ARP, OSPF) will go out on the wrong antenna. Furthermore you are likely to blow up the card amplifier when trying to transmit out of the connector not attached to an antenna because of impedance issues.
Since I have only one antenna connected to the card (to the MAIN connector), I have taken off diversity and specified to use antenna 1 for both reception and transmission. This is what you gotta do (for wifi0):
sysctl -w dev.wifi0.diversity=0
sysctl -w dev.wifi0.txantenna=1
sysctl -w dev.wifi0.rxantenna=1
To save these settings, add them to /etc/sysctl.conf.
PS: For the R52 and R52H antenna 1 correspond to the MAIN connector, while antenna 2 corresponds to the AUX one.
After having applied this, I could noticed a ~10dBm gain in reception when no obstacles are present between the two antennas and a 5dBm gain when obstacles are in the middle. I really suggest to everybody to turn diversity off because otherwise your antennas will try to transmit out of the not connected connector.
Antenna diversity is treated here on the madwifi website:
http://madwifi-project.org/wiki/UserDoc ... aDiversity
Cheers,
Stefano