FIOS definitely uses the SAME TV Channels as Cable, including many of the SAME Cable boxes. If you try to combine weak OTA signals with very strong FIOS RF Coax Signals they will be squashed. AND, since you have connected an ANTENNA to the FIOS cable, even with 20-40 dB Reverse Isolation in an RF Combiner, the very strong FIOS RF signals are going to be splattered all over the radio waves, potentially interfering with OTA reception, and also AIRCRAFT flying overhead....until an FCC Strike Team beats down your front door...