# 3 GHz SMs with high B/A ratio
**URL:** https://community.cambiumnetworks.com/t/3-ghz-sms-with-high-b-a-ratio/107353
**Category:** PMP
**Created:** [October 15, 2025, 12:12am UTC](https://community.cambiumnetworks.com/t/3-ghz-sms-with-high-b-a-ratio/107353 "2025-10-15T00:12:50Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Ken\_Hohhof](https://community.cambiumnetworks.com/u/Ken_Hohhof)
#### Post date: [October 15, 2025, 12:12am UTC](https://community.cambiumnetworks.com/t/3-ghz-sms-with-high-b-a-ratio/107353/1 "2025-10-15T00:12:50Z")
Has anyone else seen this?
We’re finding a fair number of 450 SMs with high B/A ratio (like 12-15 dB) only at the SM, not at the AP. I figured they are getting old and it was a hardware failure mode for P11 SMs, but we replace them and nothing changes. We even replaced one panel style SM with a 450i SM and nothing changed. The first one where this happened was a 450 panel and we replaced with a 450b high gain and that fixed it, so I’ve been assuming hardware failure. That assumption is questionable since replacing with another 450 SM isn’t working, nothing changes. All our spares at this point are used, but they were working when we took them out of service.
OK, maybe it is trees infringing on Fresnel clearance, but why only in the downstream direction? Most RF path issues affect both directions.
So now I’m starting to think maybe there was a firmware issue at a certain rev that only affected the older SMs, but I’m not seeing anything in the release notes, and going to 24.2.2 doesn’t seem to help.
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### Author:  [@jnovak](https://community.cambiumnetworks.com/u/jnovak)
#### Post date: [October 15, 2025, 2:18pm UTC](https://community.cambiumnetworks.com/t/3-ghz-sms-with-high-b-a-ratio/107353/2 "2025-10-15T14:18:45Z")
I see the same thing sometimes, but moving the unit closer to the tower and it works as expected. I don’t think it’s strictly failure/radio related - but I’m not sure what it could be.
\*edit
Oh, I also think I’ve seen this resolve itself one time after I changed the channel on a AP. I’m assuming it was interference from VZW, as the operating frequency was 3690. I think I moved it down to 3660.
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### Author:  [@system](https://community.cambiumnetworks.com/u/system)
#### Post date: [October 15, 2026, 2:19pm UTC](https://community.cambiumnetworks.com/t/3-ghz-sms-with-high-b-a-ratio/107353/3 "2026-10-15T14:19:06Z")
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