Hi there,

is possible with RB411UAHR to use an external antenna to get a better signal for 3G?

Apparently only antenna connector for Wi-Fi.

There are no 3G connectors on this board. You need to use a miniPCI-e 3G modem with this routerboard that has antenna connectors.

Thanks for wall your answers. What about the miniPCI you posted? Is that an external connection to a 3G antenna? Is that a Mikrotik board?

minipci-e 3G modems have ufl antenna connectors, and you can use a pigtail to connect any antenna. You will find supported 3G modems on mikrotik wiki, but mikrotik does not produce 3G modems.

http://wiki.mikrotik.com/wiki/Supported ... e#3G_cards

without the miniPCI modem you have no 3G on this board. Modem is required to have 3G. Antenna connectors are on the modem itself.

Can you suggest me a compatible modem with an external antenna with the highest gain?

antennas are always sold separately. here is a list of tested modems:
http://wiki.mikrotik.com/wiki/Supported ... e#3G_cards