Satellite diplexers are used outside to combine and then separate two separate RF Bands: The 950 to 2150 MHz from the Satellite LNB(F) and the Cable TV or Antenna TV channels. The First would combine these two bands for conveyance via a single RG-6 coaxial cable on one side, and then a second satellite diplexer is used on the other to separate the combined signals for connection to separate these Bands for Input to receivers and the like. Some Satellite Receivers will have Diplexer/Separators built in (Confer with your Installation Guide or Spec. Sheet). Satellite diplexers eliminate the need for extra wiring thereby reducing the cost of labor and installation materials necessary to run two separate coaxial cable drops to carry each signal source independantly.
If you have Off-Air Antenna TV Signals mixed with the Satellite Signals, you will need "Wideband" Splitters that have a minmum start frequency of 50 MHz and again, pass up to 2050 or 2150 MHz. (depending on Service). Those Splitters that have a Start Frequency of below 40 MHz are used for carriage of both Satellite and Cable TV with Return Band two way services like H-Speed Internet Broadband Modems and Set Top Pay-per ViewTV Converters.
Conversely, regular Cable TV Antenna Signal Splitters have a start Frequency of 5, 40 or 50 MHz. and a Stop Frequency of 900 or 1000 MHz. (1 GHz.) You could utilize any of those Splitters for distribution use of the Output Signals of the Satellite Receivers to other TV Sets.
When Supplementing your Satellite TV Antenna Installation with additional Components, consider Grounding. Dual F Port Grounding Blocks specific for Grounding un-wanted Electrical Surges and Strikes away from the LNB(F), Satellite TV Receiver and TV Set(s) are available. See the "Drop Ground Blocks" Category. Consult your Local Building Code and NEC for guidance to Properly Grounding your HD TV Antenna, Satellite TV, Cable TV, WI-FI, Wireless Internet, Business Band, CB or Amateur Radio Antenna Installation.