I have 40 or so clients on 900 using MT and SR9. Everything was fine until one day everyone's ping times jumped to 4 digits. I have tried changing channels (2 only with 802.11b which is another issue) but no help. Noise floor is a -94, not great but customers have -80 signals or better yet poor pings. I'm running 532 AP with 133/411 CPE's, all Mikrotik 2.9.x and SR9 cards.

Interference

Several people have posted that they require better signal with 900MHz than with 2.4GHz, and I agree.

900MHz is so prone to interference, and I've seen the noise floor jump 10dB, your SNR will go to hell quickly. Noise here will go from -96 to -89 regularly, worse than that on occasion, so if I had anyone with a -80 signal, their link would become unstable if not cut out completely.

B works so much better against noise than G, if you're still having those problems, you might want to invest in a cavity filter, but that also depends on whether your noise is in band or out of band.

How high is your AP? Are you using HPOL or VPOL

I put in a cavity filter today, helped a little. It probably didn't help $300 worth. The AP is 200' feet up and running HPOL.

200' up is going to hear noise for at least 100 miles. You are already HPOL. Thats a tough one. I personally wouldn't run 802.11 based 900mhz but that just my opinion.

Have you tried playing with the ack timings at all?

We have found that -80 does not make for a reliable link on 900, especially on a loaded AP. There are other potential factors such as noise floor and broadcast traffic that will negatively impact sector performance. If you could post your setup, perhaps we could offer suggestions.

I tried a Ubiquity cavity filter, it helped a bit. I worked with the local utility who was causing the interference. Better now.

Also, 40 customers on any AP is quite a few.... I find that with 900mhz, they show symptoms of overloading much earlier than a 2.4 AP does. I never run any more than 20 clients on a single 900mhz radio as things start running poorly with any more than that. If every customer were -60 signal, it probably would be better, but the more you have in the -80s, the less total you can run.

I would likely agree. We have moved to smaller cells, shorter towers with 900.