Antenna for VM130

Hello,

I have only one place to install the VM130 receiver and its short antenna wire.
But it is shielded by the aluminium Rolling shutter (specially when closed) and numerous steel beams.
The remote control only works on 3m.
Where can I connect the ground of a coax 50 Ohm cable for an external antenna ?
Thanks.

Ok
I found the reply in the détails of Vellemen kit RX433N (900-6895)
The ground is connected at 1, 6, 7 and the standard antenna furnished at 8 (wire of 30-35 cm)

Albert