Hi, "kev" and thank you for taking care my problem.

First, I only tried channels 1,6 and 11 which are loopback channels. I
didn't tried another channels because of being unsure of stability and
performance of channels excluding 1,6 and 11.

The unluckiest thing is that i have a lot of wireless routers and
networks of course around my building of my neighbour's.

I'm sure i'm dropped because when this drop is experienced eventhough
it seems connected in system tray or in apps, i connect Cat5 cable and
connect to router over cable, then i checked "wireless client list" of
router and my notebook disappears in the list. That prooves wireless
drop. When wireless is stable and normal, my notebook is listed in
"wireless client list" of router.

Signal quality goes between -50dbi and -60/65dbi with no change of
router/notebook placement.
Noise level does not go worse than -90dbi.

Anyway i'll keep using other channels, but is it safe and stable using
channels except 1,6 and 11?

I'll inform the advancements.

Thanks...