Use ethernet port with broadcast antennas OFF

Hi folks.

I got this EX3700 with the idea of using it join my existing network and then connecting my desktop to it via the ethernet port.  It was my understanding from the documentation that broadcasting the extension network was something you could turn off or on.  Having the extension network on is disrupting my existing network and dropping performance everywhere, and I dont really need it.  I just want the ethernet access port.  But when I turn off the broadcast antennas it seems to turn off everything, and I get no connection from the ethernet port either.  Is what I want to do not possible?  Do I HAVE to broadcast the EXT networks in order to have the ethernet port active?  Am I trying to do it wrong?  

It works fairly decently when the EXT networks are on, but all my other connections are showing major interference and performance hits (I'm not sure why exactly, but before I spend a week troubleshooting that, I would rather just turn off the extension networks) To make it clear, I just want this thing only as a RECEIVER for a wired ethernet connection.  was I wrong to think it was possible?  Thanks for any help or advice.