An indoor ski slope comprises a continuous peripheral wall and a floor which extends obliquely downwards relative to the peripheral wall. Raw and cyclical power measurements of a received signal are processed by the AGCCCA circuit to determine whether a current received signal process should be halted, and a new signal acquisition sequence begun. The coupler member comprises a front segment fixed to a rotor of the first slider member, a rear segment extending from the front segment toward the second slider member, a threaded part of the rear segment extending outward through a rotor of the second slider member, a control knob screwed on the threaded part and a spring interposed between the rotor and the control knob.