Why would there be interference 3550-3700 and also 3700-3800?

Who even uses 3700-3800?

The attached SA is from an existing 450 sector, it shows the entire CBRS band wiped out in the upstream direction, AND the entire 3700-3800 band. Is that even possible?

I don’t think it’s an equipment malfunction. An adjacent sector also sees the 3700-3800 interference. I’m not trying to use those frequencies, it just seems like a clue to where this might be coming from.

I see you did a scan at 20 MHz. To get the best granular view on a 450 Spectrum Analyzer, I recommend doing the scan at 5 MHz.

The 450 Spectrum Analyzer scans the entire channel bandwidth and reports the highest power for anything in the bandwidth, so can be a little misleading. Might help get a clearer picture of what is going on.

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Thanks Charlie, I’ll try that (obviously doing an SA from the AP disrupts service).

But even so, don’t you find that SA extremely strange? Strong and flat across CBRS and also 3700-3800? Who would even be using that band, is that C-band?

We did have a 450b in PTP mode one time with a hardware problem, like it had a high noise floor across the band, but I don’t want to jump to the conclusion that we have an AP that has gone bad.

Are you running Spectrum Analyzer on all the APs at a site at the same time? That is most definitely recommended. I’ve seen a AP close in proximity will desensitize the receiver and throw off the results, but not sure if that is what is happening here.

As far as the band goes, I’m not familiar with it, maybe others can chime in.

(Skip to the end for the tl;dr)

So at 5am this morning I ran SA on all 4 sectors simultaneously. I didn’t want to change the AP channel width to 5 MHz and mess up all the SAS grants so I let it run at 20 MHz.

I am attaching all 4 sector results. Doing the SA without the other sectors transmitting didn’t change anything.





I think these are real results, not a bad AP. Googling for 3.7 GHz band, it looks like that C-band and the big winners in the auction were AT&T and Verizon. So I think maybe I’m looking for an AT&T or Verizon celltower east or southeast of this tower, but there’s probably not much I can do about it.

We don’t have any PALs in this county, the PAL holders are DISH (3), Comcast (2) and Mediacom (3), but last spectrum inquiry I did came back none of them were in use yet. I am guessing that, as I expected, the mobile carriers are using all available GAA channels in CBRS up to the full 150 MHz. This would work for them since they use CBRS for carrier aggregation not the primary channels.

PALs would only help us if a secondary market develops. This is a fairly large county on the edge of our service area and no way we could have bid on the entire county. Even if a secondary market develops, I’m not optimistic that DISH, Comcast or Mediacom will be subdividing or leasing out their licenses. When they look at spectrum, they are probably like Scrooge McDuck swimming in the cold coins in his vault.

So I’ve heard people talk like switching to 5 ms framing allows co-existence with LTE, is this true? Unfortunately I fear we would have to do this at all 4 sectors and then our nearby towers and basically would have to switch from 2.5 to 5 ms framing across our whole 3 GHz network. But would this even help with our situation? Our problem is almost entirely interference into the AP, our downstream SNR and modulation is good.

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