Q :I Just purchased an FTA receiver and I will like to stay with my local cable network/antenna service? A: The Satellite Diplexer: A Seamless Solution! Satellite programming may not offer local network or independent TV channels in your particular area. Fact of the matter, there is a large portion of rural America that is not covered. The solution is actually quite simple: capture those signals with either an
off-air (uhf/vhf) antenna or cable TV feed and add them to your channel line-up.
You can run two lines: one line from your satellite dish and the other line from your local channel source OR you can use two signal
diplexers and run both signals down ONE coaxial cable line SIMULTANEOUSLY
(Diagram 1). One
diplexer is used outside to combine the two separate signals (one signal from the satellite dish and another signal from either an
off-air TV antenna or cable TV feed). A second
diplexer is used inside to separate the combined signals before they enter your
satellite receiver (Diagram 3).
Satellite diplexers eliminate the need for extra
wiring thereby reducing the cost of labor and installation materials necessary to run two
coaxial lines.
Combining LNB and Antenna/Cable through 1 Line
Diagram 1 
Combining LNB with Antenna/Cable Through a Multiswitch

Connecting Diplexer To Satellit Receiver
Diagram 2