So what is a VHF/UHF diplexer, why you should care? These are different types I removed recently.
A diplexer is a different device than a passive combiner or splitter. The ports of a diplexer are frequency selective. When analog TV signal is gone, this thing is no use but causing troubles because it tell digital signal to go through a certain frequencies to transfer, which is absolutely not necessary.
Together with the stretch VHF antenna, this piece of box has to be removed.