Hi Guys!
Yes it is good advice to place antenna high and without obstacles I agree. But I still think is something with connectors(like you said swarg_eu), tried to solve it and need to test more.
For testing I used 3 antennas in the same spot a few cm from the window. They were directed at the same or similar spot. I used linux software linSSID, which has nice graphical representation of signal quality and min, max ranges. The adapter was Alpha NHA. The antennas were: Alpha 5-7 dBi omni directional stick, Alpha 7dBi directional one and 18-21 dBi directional square panel antenna.
The omni directional stick performed the worse. Suprisingly 21 dBi one performed worse than 7 dBi directional. The 7 dBi directional was pretty good one. I get a lot of signals from different directions, much more than from 21 dBi one. If I point it in the same direction as wifi router is positioned in the house(different room, different floor) I get great signal quality, better than from 21 dBi one. In longer distances the quality varies. In some cases if I point panel 21 dBi antenna in the right direction the former wins, but not always. I am really suprised that if I point larger 21 dBi antenna from window to another neighbor house, which is 100m away without obstacles I get only 80 PWR tops on airodump or linSSID. I was expecting much better signal. 7 dBi panel antenna gives me 76 dBi tops and seems more consistent.
The problem is most likely cable, however,.... I am still searching online stores to buy direct adapter so I wouldn't use any cable. I need male BNC from antenna and female SMA to adapter. It is almost impossible to find one, been searching it a lot. The problem is female RP SMA, beacause I can't find the right one, so I could screw the adapter on it, the thread has to be the opposite.
I have been searching https://www.tme.eu/en/, but haven't found the right one. If someone posts a link to eu based store so I could buy the right one I would appreciate it!.