I have another question. Is it possible to use just a standard two way splitter as a diplexer? I want to do some dxing and just wondering if I can use stuff I have around the house.
Simple answer NO. The regular CATV splitter you have around the house won't work for Satellite (different frequency range). The Diplexer splits the signal going through it into a CATV signal / Sat Signal. Also, it allows the DC voltage to pass through the SAT side which is necessary to operate the LNBF.
I want to bring the rooftop antenna into my room from the multiswitch. I currently have all the sats hooked up and the antenna hooked up. Am I guessing right is that I need a diplexer in my room to seperate the two signals?
Keep the pre-amp on the same side of the di-plexer with the antenna. Remember your Sat Receiver sends a voltage up to the LNB!! so if you allow DC pass on the antenna side that Sat voltage will also go that way !!
If you use an OTA antenna that requires a powered amplifier, the amplifier must be between the TV and the diplexer. That way the signal coming from the OTA antenna, will pass through the diplexers, then go through the amplifier into the receiver. No power will pass through the ANT side of the diplexer (it is blocked).