The CHANNEL PLUS 2512 DC + IR Passing 2-Way Splitter/Combiner is not a UVSJ. The splitter is allowing the two antennas to 'fight' each other.
A UVSJ is a tuned filter network, not a mere splitter in reverse. It will have a port that passes only UHF frequencies, another port that passes only VHF frequencies and a 'common' / 'combined' port.
Try a real UVSJ:
http://www.solidsignal.com/pview.asp...nna-%28UVSJ%29
http://www.radioshack.com/product/in...ductId=2103923
http://www.amazon.com/Antennas-Direc...Direct+UHF+VHF