In the case of the LANCOM devices OAP-54-1, OAP-321 and OAP-821, the act of connecting an external antenna to the antenna connector causes the integrated antenna to be disabled by an internal pin.

The pin in the antenna plug is designed so that it triggers a contact in the antenna socket, which disables the antenna that is built into the lid of the device.

The blind cap does not disable the integrated antenna, because its pin is not long enough to trigger the contact in the antenna socket.