Two. The 15km transmission distance can only be obtained under the FCC standard when calculated in an out of doors natural environment without having interference. The SRRC standard is adopted in mainland China, and also the furthest transmission distance is 8 km. Mavic 3M with RTK module for centimeter-degree positioning. https://m3mhomes.com/commercial/m3m-route-65-sector-65-gurgaon/