Cutting the cable, lets talk options and media setups

ok, somebody splain this Lucy. I bought a flat antenna piece to run under a window and get my powered Antenna outside. But after I moved, the only channel I have issues with is NBC and I didn't care enough to run it. So I get home today and the channel is bad enough that I would be aggravated watching the game. I moved it around inside the house with no luck. So I break out the piece, run it through the window, unplug the antenna from the Firecast and bam, I have perfect reception with no antenna. How can I have perfect reception without antenna but plug it in and it cuts out?