5GHz Wifi Spurious Emissions Between Access Points?

Wireless newbie here…

I have a router (R1) with (4) vertical external antennas and an access point (AP2) with 4 vertical external antennas placed at ceiling height on the same wall to extend coverage to a couple of adjacent rooms. Literally all the antennas are lined up 10' apart at the same height on the wall such that it's

l l l l - - - - - - - - - - l l l l

When I purchased the router + AP combo the vendor swore up and down the appliances wouldn't interfere with one another so long as one was operated on channel 36 and the other channel 165.

When appliance (R1 or AP2) transmits traffic with a single client (C1 or C2) it does so at 55MB/s. Sadly when both (R1 or AP2) pass/transmit WLAN traffic for 2 clients at the same time the achieved bandwidth drops to 5-10MB/s. To be clear C1 is connected to R1 and C2 is connected to AP2. The clients are just doing an iperf3 file transfer among themselves.

As soon as I placed R1 on the floor and out of line of site of AP2 (some boxes of stuff attenuating) the achieved transfer is 55MB/s like one would hope.

I don't have any reason to believe the vendor had a batch of units with bad band-pass filters causing spurious emissions outside of the spectral mask. When I check the FCC docs for the appliances, the FCC shows pass for "frequency stability" and "spurious emissions" at a 3M or 9' test distance which is akin to my setup.

Because of attenuation to necessary coverage areas I really do need to place these appliances on the same wall, near the ceiling no more than 10-14' apart.

Is there a wireless principle I'm unaware of that explains why R1 and AP2 are diminishing each other so greatly when transmitting at the same time even though the channels are "supposed" to be completely isolated???

Is placing a small strip of RF shielding fabric obstructing the line of site between the router and access point a feasible solution???

I think a strip of RF shielding fabric between them may look tacky but if that is the only solution I'll gladly do it. If that is a feasible solution does anyone here recommend a particular RF shielding fabric to buy???

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There's a typically sensitivity of about -65dBm to in-band non-WLAN signals for carrier sensing. The side lobes of the transmitters need only attenuated by about 40 to 50dB. So, if another AP in the nearfield is transmitting with 20dBm, there might still be side lobes with -30dBm. The additional attenuation by 10' distance is not that big, so the first AP is receiving this noise and thinks: Channel used by somthing else, thus waiting for the channel getting free.

Discovered this when having 2 APs in the same distance like you and got a lot of DFS radar errors at both APs like a bulk of radar head missiles is targeting me.

You can try a metal sheet between the APs but I'm not sure if the clients aren't radiating out-of-band noise also.

Hard to judge without a spectrum analyzer

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Andi. You sir are a gentleman and a scholar!

New units Linksys shipped me behaved the same. I opted to try a pair of Ubiquity Unify UAP-AC-PRO instead.

At the same 10' distance the achieved throughput is only 20% diminished instead of 90% diminished with the Linksys units.

For those interested, I even placed the Unify units immediately beside each other and the achieved throughput was only 54% diminished.

My hat is off to Ubiquity!

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