External Antenna for FG 40F-3g4g

[MarcP1]

Hi,

have got a problem with the signal of my mobile internet at a site.

The sim card is recognized by the system, but seems like there is no 4G (lte) signal, as the FG is not able to connect.

Now I am thinking of using an external antenna or at least an antenna to put as near as possible to the outsite wall. 

Right now the 40F is in the rack, which I assume, is the problem.

While searching for a solution I saw many suggested an extender, but I don´t want to use an extender, as we had so much trouble with them. 

Specifiyng my question:

Is the a recommended antenna?

Any specifications, if I need to use a long SMA cable to connect the default dipole-antennas?

Thanks for your help.

Regards

Marc