NIce Shel 50 - how do you extend the range of a remote control without an antenna socket?

Welcome,

I have an NIce Shel 50 operator, behind a sectional door. It is possible to open the gate with the remote control from a distance of approximately 35 metres, and I would like to extend this range by installing an additional antenna. I would like to extend the range by installing an additional antenna, but I have heard from a Nice technician that this model does not have a socket for connecting an external antenna. The remote control can be operated from a distance of approx. 1.5 m. I would like to extend the range by installing an additional aerial