Cant connect SM deregistered - No GPFs from AP

Hello i have a problem “SM deregistered - No GPFs from AP. Check signal level and intereference on channel” what can i do to fix it?
I Have 2 AP, they stand back to back with 1 frequency.
From south side i have 10 SM’s connected to south AP-1, and everything is ok.
From north side i had 1 SM connected to north AP-2, but after it broked out i have tried to change it for ePMP 2000 in subscriber mode (cause i have only this one) and we changed connection place.

The distance between AP-2 and north-SM is about 15 km.
I use:
AP’s - ePMP 2000 with sector antenn
SM’s - ePMP force 200
and north-SM - ePMP 2000 with sector antenn

And here i tried connect to the northAP-2 from 10 km

no gpf is telling you that the SM can not decode the AP sync signal that is in the beacon frames.
There are a few reasons but start at your APs and make sure that they are using GPS or CMM timing, one is set to front and the other is back. Both are these are the same: frequency, max range, SM target RX level frame size, frame ratio and channel bandwidth. You may need to enable Co-location mode if there are other radios on the tower that are fairly close.
Make sure your AP sector antennas have good cables with good connectors on them, these are easily damaged by tower techs that are in a hurry anso make sure the antennas are not too close together back to back, each manufacturer provides a radiation pattern that will show you how strong the back lobe is and you need to ensure that the antennas are within each others back null and not within the back lobe.

on the SM side, you need to use the correct SM radio for the distance. An F180 is great for up close and generally out to 5ish KMs, but that is also dependent on what your area is like and what kind of vegetation is in the way. Personally, skip the F190s and use a F200, the cost to performance isnt there for the F190s. I know its more expensive but consider just getting the F300 radios to prevent replacement should you need to upgrade your APs to epmp3000’s. The F300-16 is comparable to the F180 and the F300-25 is a direct replacement for the F200-25 and the F300-19 is a decent in between radio that is good if you just need a few DB more. There is a cost difference with the F300 over the F180/200’s but you wont have to worry about swapping out at the time you upgrade your AP’s and you will be able to take advantage of Mu-MiMo right away.

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Just to add, if you set the AP range to 10km, DONT try to add an SM at 9.9km, it has a high chance of failing to connect. Sometimes it will say no gpfs in the wireless tab for that AP. If you need 10kms then set to 11kms.