If necessary you can do it with a diplexer as Jonn said . I did until I saw the following diagram.
What Winegard calls a "power supply" below is the wall plate with the antenna booster switch and LED showing when the amplifier is on.
If you still want to be able to use the external cable in for both cable TV and the external dish just add an A/B switch to switch the incoming coax from the sat receiver "sat input" to the sat receiver "TV input".
If your receiver doesn't have a coax output (and many new ones don't) and you still want to use the batwing antenna you will need to use an A/B switch to switch the signal between the receiver and the antenna out connection on the wall plate.
One thing not shown in the diagram is using the RCA type connections or the better quality "component" type output or the HDMI (best) output between the sat receiver and the TV.
That will yield a much better picture with no interference from any local channels. You have to select a "video in" with your TV menu instead of using channel 3 (for example).
Some newer satellite receivers don't have a coax output so you may have to use HDMI or component connections.
If you have a video distribution box that will have to be taken into account.