In day time speed is low 2-4mbps and in the evening it grows up to 15mbps without any modifications!
AP is a RB133 with only 4 clients and i tried ROS 3.10 and 2.9.51. With 3.10 the signals drop suddenly one day and never recover…from -55…-60, to -75 to all clients. After downgrade to 2.9.51 the signal is back to normal. The CPU dont rise more than 60-70% and there are 2 wlan cards (2.4Ghz - R52 and a Gigabyte). The case is big (400x300) and well ventilated. Why is the speed problem? All the client use RB411.
What sort of terrain have you got?
Swampy with alot of water/moisture?
Sea in the back of the sectors.
I have another RB411 in a separate box, with 24dBi grid that is not affected and a 5.2Ghz link in another separate box that is not affected as well.
Antennas are in the black circle.
Maybe some other user is taking over 2.4GHz for their own purpose. What is your CCQ during the day? CCQ during the night?
I got a similar problem with 4 links serving an island 15km of sea from the main land. I’m able to make 100%/100% CCQ links (one of them is a 35km link with an awesome CCQ).
But.. randomly those links go down. -90 signal, 30%CCQ,disconnections. Then suddendly back to normal after 20 mins…
It’s impossible there’s something between them, neither the Titanic is high enough to disturb that link.
It’s not heat related, since this happens in the middle of the night too.
Machines are all far from each others like 3 meters.
I tried to use 5ghz-10mhz but even it’s sightly better, i continue experiencing the same issues.
RB532s and RB333 - all with ROS3.10 with noise immunity. Frequency not used by anyone.
Even everything looks perfect for 20 mins (after i recalibrated everything), it mess up after a while…
Might it be the same problem of InoX?
Perhaps some sort of problems with the tide?
Different reflections depending on wind/tide/waves, …?
Sorry, just a guess - this CAN in theory kill your links, but I’m living several hundred kilometers away from any sea, so no first-hand experience 
As the suface of the water heats up with the sun, thermal evaporation can occur which can potentially take down links over water.
In these instances you want to dipole your links.
My links are not over water…water is behind.
InoX,
Your problem is best solved using a spectrum analyzer.
Must be some sort of noise at those times.
Is that a hotel your antenna is on ?
If so, check if they are using DECT phones/ microwave ovens near the top of the tower… Might be just that.
Or, do they have a hotspot installed in ?
Must be some kind of noise out there.
when i do a scan , i found at least 10-12 ap’s 
but these ap’s work in the night too…
This problem happen to me too…it’s always happen at 2 - 4 AM time range with 15-30 minutes of duration. It’s not regularly happen but if it happen again, it will always happen at the same time. My normal CCQ was 80-100% both TX and RX at my PtP link. When it happen, the CCQ will drop approximately at 20-50% in both radio. The same as my signal strength, when it’s normal, I have -53 - -58 of signal strength. But when it happen my signal drop to -72 - -88 then i got disconnected. One thing make me confused is my ACK timeout is still the same at 22. I currently use PC box for this 18 km PtP link (12 - 20 mbps of traffic at the day, 3 - 7 mbps of traffic at the night) with specs :
- Intel Pentium 4 3.0 Ghz
- Motherboard Gigabyte with i945 chipset
- PCI to MiniPCI converter
- SR5
- D-Link DGE-530T
- Band 5Ghz-turbo with nstreme and polling exact-size
This link was established for about 8 months. This problem come to me since three months later. I ever see this issue when I’m still using RB532A for this PtP link, then I decide to replace it with PC box, the problem gone away. The question is, why should this happen always at early in the morning when my traffic is low?? It never happen at the day time. Somebody know what should I do? Is there any interference with the other? I really don’t know what caused this problem 
Your help really appreciated 
Regards,
WAP4-AP
Monitor the voltage at the AC source.
My guess is that there is a significant load on your power grid during these times, and your voltage is dropping.
If you use 12v power supplies try switching them over to 24v or 48v.
Running on UPS and first at 24v and now at 15v. The same.
monitor your noise floor…i just think its either some interfearence or some one using a link only during business hours.
we see the same thing here, but after analizing with a spectrum analizer we found various noise sources during business hours
+1 to that.
Also, see with snooper what kind of traffic is on those “neighbours” of your on different times of the day, maybe helps.
In the daytime SNR is 32 and in the night is 45. From what could it be?
Is this from noise floor, or signal level ?
Whatever it is, is afecting you. I see this on me, and in the night noise floor is 2 to 4 db lower than during day. But such a difference, is big.
Posibly cordless phones, microwave owens, all kind of stuff. Even air conditioners, some have remotes in 2.4 open band, not in infrared. Lots and lots of thing active during daytime.
Also, usually traffic on your wi-fi neighbours is reduced, so interference from them is reduced…
/agree in day or at nite the diff in signal is almost always due to someone elses noise factor. THis coud include but not limited to microwaves, 2.4 5.8 900 mhz phones, all power lines, any kind of lights for stadiums or street lights, noise from other wireless networks. Finding out wher your noise is coming from will be best acheived with a singal analyser. They are not cheap, most do 900 or 2.4 or 5.8 or rf, most dont do all of the channels they start at thousands up to 10s of thousands. Have you tried diff channels? diff channels can take in diff noise in some cases. And then ther is the no brainer making sure that your immediate area isnt have some daily malfunction like someone right around you running some scanning tests or radar or even some power line near you that gets used in the daytime but not at nite