Hi,
receiver is not necessary. The unit has to be only powered and RED light must be steady ON on the Spirit unit.
This mean that the Spirit Settings should be started after the unit is initialized.
This guide can help you:
http://manual.spirit-system.com/index.p ... er_WindowsWhen you unplug the USB interface, can you check which COM port is disappearing? For this the unit can be disconnected.
COM port that will disappear is one that is required for communication - this must be selected in the Connection tab. But normally it is automatically detected.