Issue with 900MHz AP

I’m having a really strange issue with one of my 900MHz APs that just cropped up over the last 3 or 4 days.

SMs will register (all have good signal levels (between -65 and -72, noise floor was around -85) and will stay registered and fully operational for a few hours. Then, all of a sudden they will start re-registering like crazy. I can’t seem to figure out what’s causing it. The only thing that seems to have changes is that the rest of the 900 band is busy in the area. The AP is running on 906 and from about 909 on up the noise floor is -71. Unit is sync’d with a syncpipe parasitic and the nearest APs are 7 miles away at 924MHz about 13 miles at 915MHz. All are sync’d with the same control slots, downlink %, etc.

Any ideas what could be causing this? I guess I would have to suspect interference, but I would think my AP would be seeing more noise than that to cause all of the SMs to drop at once (including the ones above the noise floor at 909 and above). I have tried setting the unit to generate it’s own sync, but the issue still persists.

After messing around some more, I’ve found that the instant you attempt to pass traffic to an SM the behavior starts.

It does not seems to happen with small packets (pings), but if I do link tests, all of the SMs will start re-registering once they are selected and a link test is performed.

Interference or loss of GPS sync.

Fairly certain it’s not a GPS issue as having it set to generate its own sync should’ve solved that straight away. It looks like it’s interference smack in the middle of the band that is making it impossible to operate at the start or end of the band. Putting my AP at 915 stabilized my SMs, but performance is not ideal.

If anyone has any other ideas, please let me know. Thanks.

Is the AP in the range of another 900 Canopy AP?

One to the east about 13 miles and one to the west about 7 miles. All were on different frequencies, sync’d and matched settings.

And I should add that the stability I saw last night is no more. It’s back to it’s old behavior again.

If you flip the AP to SM mode and do a spectrum analysis, what does the spectrum look like?

When the other APs are off, I see noise up to about -71 from about 909 to 921/922. After that it is a sharp fall and 901-908 are -88 and 923-930 are -88. It’s definitely something in the middle of the band. If I try to run the AP in 906 or 924, I cannot get the SMs to register. If I throw it right in the middle of the interference at 915 they work for a short while.

Prior to Tuesday or Wednesday of last week, the spectrum was very quiet. I just can’t understand why I am unable to work around it and even my SMs with very good signals (I upped the power and got them to -58 at the AP) won’t stay connected. Does not matter if I generate sync or sync to timing port (syncpipe).

By other AP’s you mean the ones at 7 and 12 miles?

I assume this AP has an omni?

You could try to determine the direction of the source of interference. You’ll need a helper.

Take an SM with a 17dB yagi to the tower. Turn off all AP’s. Set the SM to refresh every 2 sec and sweep the area while your helper monitors the SA yelling out the highest dB level. You should be able to determine the approximate direction. The more time you take, the narrower your search will get.

Good luck.

All three of them are using omnis, yes.

That’s what I was afraid of - this AP is at the top of the head house on an elevator - very tough to work on. Will be interesting.

Thanks for the help.