@Corenti 

Hi, the two external antennas on MR600 v3 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. In principle, it’s not recommended to replace them, because the antenna is only used as an auxiliary, and the strength of 4G signals mainly depends on SIM card and ISP.
If you think that the original 4G antenna is not good enough or you need to change outdoor antennas, please pay attention to the following information:
1). If you want to change, please change two antennas at the same time, and the two replacement antennas should have the same specifications
2). For the replaced antenna, the interface type needs to be matched. The interface type of the two original antennas is SMA plug, that is SMA male
3). The frequency range or band supported by the replacement antennas should be the same as the original antennas. For MR600 V3, it is 790-960MHz&1710-2690MHz.
4). The distance between the two replacement antennas shall not be less than the distance between the original antennas.

Note: Since we are unable to guarantee the performance of third party antennas, we are unable to guarantee the performance of the device after you installing third party antennas.

Your understanding would be highly appreciated!