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bpwl
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DFS false positives caused by hAP ac2 and wAP ac ??

Sat Feb 15, 2020 12:06 am

HI,

I have a very rare DFS radar detect after 4 months on a deserted holiday resort. Strange, why did it happen?
While digging for a possible cause I had some disturbing scans on the 5 GHz band, that are repetitive in outcome, and make me worry.

Story is, on 1 directional PtMP link with a SXT sa5 ac (to client SXTsq ac's) there was a lonely radar detection. The SXT SA5 moved up in the channel list from 5540 MHz to 5660 MHz, just as planned. But is was not expected to happen. The resort is deserted, with 20 houses connected via PtP (and some 100 neighbourgs but also deserted).
Scanning the 5GHz showed almost everything switched off by the neighbourgs except 1, and the 20 houses where well under control. All 5GHz channels are 20 MHz Ce, that is 40 MHz.

Except a hAP ac2 in number 7 was ALSO visible at 5540 MHz, though it was set at 5220 MHz. What's this ????? Measurement was done with the wAP at the same house 7.
The reverse scan by the hAP ac2 showed the similar scenario. The wAP ac was operating at 5180 MHz , but also appeared at 5500 MHz.in the hAP ac2
Changing the freq of the wAP to 5220 MHz , made it being added to the scan list at 5220 MHz , but also at 5540 MHz.
5540MHz being the working freq of the SXT sa5 pointing obviously in the direction of house 7, and having the one "radar detect" , that I beleive is just a glitch.

The wAP is not yet mounted outside, so the signal between hAp and wAP is (very) strong. Reducing the TX power on hAP and wAP reduces the received signal strength accordingly.
But the fantom higher signal remains at the same level.(-83 dBm). And that worries me. Having fantom frequencies because of overloading the receiver should dissappear when the TX power is reduced. Or is this radiating from the hAP and wAP bodies ? Is it always there? Is that a possible reason for the false radar detect?
Klembord-2.jpg
As Ron Touw tells here at the 1 hour point in https://www.youtube.com/watch?v=ZbrbRUAfpac . Reflections that at the transition from sending to receiving create a signal that resembles a radar pulse.
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