450i CBRS - All SM stuck at 1x - bad hardware?

[Jacob_Turner]

We hung a new CBRS AP at one of our sites last week and attempted to move customers over to it yesterday. Unfortunately, all SMs end up sticking at 1x on TX and RX most of the time. Randomly, they will jump to 8x as expected but then plummet to 1x and stick there. Eventually they de-register and will stay disconnected for hours at a time. I was only able to leave one SM attached to play with, but this is feeling like a bad AP to me unless there is some magic I’m missing?

Spectrum is squeaky clean at the AP and at station locations. This SA capture is from the AP when SMs are stuck at 1x. SA captures from the SMs are even cleaner.

Stations report good SNR even with the bad rates:

Every now and then rates return to what I’d expect, but only briefly.

I have tested different frequencies and widths (20 and 40Mhz) across the band and the behavior is identical. Half the time SMs won’t even register and have a high re-reg count.

There is an old UBNT M2 sector about 3’ below this AP and an ePMP 5Ghz sector below that. Otherwise, there is nothing else on this tower and no CBRS gear for miles.

The behavior is the same on 22.1.1 and 22.2 firmware.

Has anyone else seen similar behavior? I have a number of sites with the same build without any similar issues.

[Eric_Ozrelic]

Do you have another AP you could try up there? At this point I’d probably start a ticket with Cambium.

[Jacob_Turner]

I will open a ticket with Cambium and do have more NIB APs I can hang - But, that also requires getting the tower crew back up there. Scheduling can be a challenge and the costs are not insignificant, unfortunately.

[Jacob_Turner]

I’m working with Cambium support on this, who also doesn’t see any obvious cause for the issue. One thing that has definitely become clear though is that there may be a temperature and humidity component to it, as the problem doesn’t exist when it is warm and sunny out. Perhaps some sort of strange and extreme thermal inversion issue that only affects 3Ghz 450i in this location, but no other equipment.

[MiahSchaller]

@Jacob_Turner

One thing that has definitely become clear though is that there may be a temperature and humidity component to it, as the problem doesn’t exist when it is warm and sunny out

Just spitballing, but if this is a 450i 3G Connectorized AP, there may be an issue with the connection between the AP and the antenna, such as moisture in the LMR connections.

[Jacob_Turner]

It’s the integrated unit and has exhibited this problem since installed, on a sunny day.