The voltage at the antenna should be 12VDC. It is very likely that you have a bad connection on the cable running from the Video Switch to the Antenna. Verify that you have 12VDC coming from the video switch. If you do follow your cable and check every connection until you find out where you're losing the 12 volts at. If you do not have 12 volts at the video switch your switch may be faulty.