Help usb install OS X 10.11

Hi guys I need some help because right now don't have other mac to create a usb install of os x 10.11 , I have macbook air with os x 10.12 and want to downgrade to os x 10.11 I tried with transmac on windows but it not see the usb , I go to my mother imac and created a usb install and see the usb when push alt on boot ,charging and then I have a interdiction sign , now I don't have access to the imac and need some help to try to create this usb on windows ,downloaded other version of dmg on torrent and want to try with . I have access to the recovery partition on the macbook air .Any suggestions , thanks ?