All users at 1x up and down

I have a situation causing the loss of quite a few customers.  This has been going on randomly for some time but lately has become a daily event. Sometimes more than once per day.

PMP450 AP with 37 SM's.  All connected with signals between -60 and -68.  Modulation is mostly 6x down and 4x to 6x up.  Frequency setting at 5780Mhz. 19dbm power and 15MHz channel size.

Once or more times per day all users drop to 1x up and down.  Suspecting side channel interference  we lowered the frequency 5Hz and rebooted. This brings them back to normal.  Sometimes within an hour they drop to 1x again.  Lowering the frequency and rebooting again by 5MHz brings them back. We have also tried raising the frequencies by 5Mhz each time with the same results.

Spectrum analyzer shows the frequencies fairly clean with a noise floor of about -75. to -78. No indication of spikes on adjacent channels to the ones we are trying to use.

I should also point out that the adjacent sector has experienced this once or twice but has been stable now for some time.

I'm wondering if I have a hardware failure even though nothing is in the logs.

Also wondering if there are signals that don't show up on the spectrum analyzer that could cause this.

I was having similar problems with a PMP450 3.65 sector that was receiving interference from a UBNT 3.65 sector. Same symptoms... my AP would work for awhile, everything seems fine, clients have good modulation, and then the modulation would crash on everyone. It could be fixed temporarily by rebooting the AP.

I ended up moving the channel as far away from the UBNT AP as I could. It's been stable since then.

The comment that puzzles me is that this interference does not show up on spectrum analysis.

Eric - Is that the case with your similar experience as well?

I would suggest that maybe scanning for a longer period of time might reveal the interference (if that is possible to do).

I have it stabilized at 5750Mhz @ 15Mhz.  Signal and signal to noise are acceptable. Seems the entire center section of the 5.7 band is unusable even though the spec an shows it clear with -75 to -78 noise floor.

I'm going to reorganize and move it down to 5740Mhz and 20Mhz tomorrow and see how it goes.

-75 to -78 being a clean spectrum depends on the environment and signal levels. You mentioned that the recieve signal levels are between -60 and -68. Lets take the best case, -60 signal level and -78 noise. That gives you 18 dB of margin or SNR level. That puts you squarely in the 4X range. Next the worst case, -68 signal level and -75 noise. That gives you 7 dB of margin and that's barely enough to maintain a link much less stable 1X. What are the peaks you see in the spectrum analysis? Its entirely possible that there are peaks in the analyzer plot that makes this situation worse. 

Anyways Eric and Matt had the right suggestions and sounds like you have already found a way around the issue. I just wanted to add some color into concluding how bad or good the noise is in this particular situation. 



-75 to -78 are the peaks.  We are replacing this AP with a medusa next week.  Will run several more scans for longer periods.  Perhaps something will show up.

Please reply when you have the 450m installed and operating... would really love to hear your thoughts.