@GTsatiris 

Hi, the following link might  provide you with some guidance:

MR600 V2 & 4G/+ Antenna Information (LPDA MIMO) AU - John VK3HJQ

  @GTsatiris 

Hi, 

By internal antennas, you mean indoor antennas, right? the external antennas I mentioned below doesn't mean outdoor antennas, but the external LTE antennas on the MR600 v1.

The two external antennas on MR600 V1 are 4G LTE antennas, which are different from ordinary wireless device’s antennas. This antenna is mainly used to receive 4G signals from ISP by auxiliary SIM card. 
If you need to change the antennas due to the original antennas are broken and device is out of warranty, here are some tips:
1). If you want to change, you must change two antennas at the same time, and the two replacement antennas should have the same specifications, because the two antennas work together. If you only change one of them, it will not achieve the desired effect, but the effect may be worse.
2). For the replaced antenna, the interface type needs to be matched. The interface type of the two external antennas is SMA plug, that is SMA male, not ordinary RP-SMA
3). The frequency range supported by the replacement antennas should be the same as the original antennas. The supported frequency range of MR600 V1 is  700-960MHz&1710-2690MHz.
4). The distance between the two replacement antennas shall not be less than the distance between the original antennas.