auto | serial | Internal | External
must be finish with a RB reboot.
beta6 have got roblems with APN… when you use default one and change his value to other one then ROS can remember old one and still use it ?!.
At telit lm940 the at-chat not work.
Sometimes change who not should do anythink with lte1 can do reconnection…
just beta system.
About Antennas config, read a this uldis answer, full post is very interesting and short 
http://forum.mikrotik.com/t/routeros-v7-and-chateau-lte12/139448/1