I havean AP sector twith 17 clients up for a year with signal strengths ranging form -55 to -75. One day everyone lost 10-15 db and many could not associate at all. I tried changing boards, radios cards, coax and antenna. Now, everything on the tower is new, same problem. I tried scanning for interference, and there was nothing else on my channel to speak of. FInally I changed antenna mode to antenna-mode=rxa-txb which makes no sense at all with one antenna connected to the A port and every client came back to their orriginal vlaues of -55 to -75. Anyone know why this would happen? It works so I hate to touch it but it bugs me that I had to misconfigure it to make it work.

Since no one has any ideas I will post some more info. This is not a good solution, "rxa-txb"... While it appears to have fixed the signal strength, ccq's went into the toilet and uploads are terrible. I did some channel searching and found another channel with less activity and now I am getting good connections again. I am concerned this may be a short lived fix and am thinking about cavity filters, different polarity, etc.

I spoke to another tech at a competing WISP and he had same issue. He resolved it using an older Senao card with the Prism chipset and even stayed on the orriginal channel where he started experiencing problems. Possibly it is an Atheros problem since I have tried three Atheros based cards and they all had the same issue. To date I have replaced everything on this sector, radio card 3 times, motherboard twice, coax twice and antenna once.

Anyone have any antenna suggestions?

sounds like you blew the little widget that chooses which input port to listen to.
CM9?

On PRISM chips, most chores are performed by the firmware.
On Atheros chips, most chores are performed by the host.
PRISM will bug the host system less but the Atheros is by far the most flexible.
If you are referring to 802.11b then PRISM will also perform better in an environment with lots of 802.11g traffic, since it has no notion of 802.11g (which it will consider noise).

Thanks for the response. I would love to use Prism but they don't support Nstreme do they?

unfortunately, no.
that would be a PRISM chipset (+firmware) limitation