900Mhz Interference

I have two sites in towns 10 miles apart.   Once or twice a year all the subscriber modules (Using the only Canopy 900Mhz integrated SM's and Advantage 900Mhz AP's) at both sites will go through fits of re-registering after about it day its over and everything is working fine.  I've never been able to track down what the interference might be but just wondered if anyone had any sort of suggestions.  My current conclusion is something atmospheric ducting or solar event but i'm at a loss.   Possible things on the list:

I'm located in central Illinois FYI

1.  Electric company 900Mhz smart meters. If thats it why doesn't it happen all the time.  This actually happened before the electric company installed those meters.

2.  Farming GPS but if this was the case I would once again think it would happen all the time.

3.  Water meter 900Mhz transmitters.

It just seems strange because the distance between the sites is large.  If it was local interference I would expect to see it impacting a single town or cell not everything at both places.

Any suggestions or speculation would be welcome.  Thanks!


You're talking about PMP100 radios right? At this point between being 900mhz, and the age of the equipment, and how infrequently it happens, I don't think there's a whole lot that can be done to troubleshoot these mystery drops. Have you tried any of the new PMP450i 900MHz gear? One of the really nice things about the new gear is that is supports 2 chains for diversity in MIMO-A mode. So if you're getting interference on one polarity (which would cause the drops and re-regs) you might not see it on the other pole, and MIMO-A might keep the link up and running. GPS sync is also supported between the PMP100 and PMP450, making transitions a bit easier. Lastly, the new PMP450i gear supports channel widths down to 5MHz with up to 30mbps of throughput, which is a considerable improvement over the old PMP100 900 radios, and it uses a smaller channel width.

How would you troubleshoot it even if it was the new equipment?


Here's a few things I would do:

- Upgrade to 13.4.1 if you haven't already

- Use google maps/earth to figure out if there are areas where groups of SM's are experiencing high re-reg's, maybe this will help find or carve out the interference

- If you're using GPS sync, make sure that you watch your logs after an incident to make sure you're not temporarily losing sync, this can cause these kinds of drops to occur.

- Try to use a narrower sector antenna or even a high gain flat panel as high F/B as possible, I like KP's options for 900

- Use a filter on the AP to clean up OOB from pagers up top, and cellular down below

- Change polarities if you haven't already tried

- Watch for SM's with the highest re-reg's, and replace them with connectorized units with high gain yagi's

- I wouldn't really spend any money on any of the above solutions without trying 450 first, as you'd just be dumping money into crusty old gear!

- Lastly, after an incident grab a support dump via CNUT of the AP and SM's experiencing the issue, send to Cambium for analysis

I wonder if its not the GPS sync.  Once again my stuff is a generation before PMP 100's you are talking about and i couldn't find any logs in the CMM listing any sync problems although I could monitor it while its happening and see if it is losing sync.  Then I remembered the 3rd small site that just has a 900Mhz Omni and no GPS and it was being affected the same way.

I did experiment with Omni's back in the day and never got significantly better results and by that I mean when I would have signal problems it wasn't so much lack of signal but some sort of noise that would cause connections to fail.  I admit yagi's to me are a pain in the ass I always liked the integrated units but thats not the way the industry is going.

I take it you use the 450's yourself.  In todays day and age with more smart electric and water meters and farming GPS systems how much better is the 450 equipment than the 100 or what i've got.  Right now with current noise levels most people are lucky to connect at 1.5M with 400K up.  On a good day its 3M with 800K up.  I hope you don't mind these extra questions I appreciate your time as I consider my upgrade option paths.