Most of the rigs with an outside cable jack, it's for park cable, NOT for sat tv
Let me ask you a question: Is there a wall plate (Same size as a standard outlet or switch plate) inside with a round hole (12 volt socket) An Antenna type connection (With wire running to your tv) a button and a light? That is a combination device, it's is both a switch (Park Cable/Rooftop Antenna) and power supply for the roof top pre-amp. IT will not pass sat tv power and signal from/to the receiver/lnb
My suggestion is this.. Open that wall box, identif the park cable lead (Should be the center one) and using what we call a "Barrel" connector (This looks like the fitting the cable to the tv is hooked to..> On both ends) and some antenna cable extend this wire to the Outside TV ANTENNA IN jack on the Sat receiver
Run the TV-OUT from the sat receiver to the fitting you just freed up by disconnecting the above mentioned cable
Run brand new RG-6 to a handy connection point,, This may be a basement compartment or a bulkhead (Through wall) connector from the LNB IN on the sat receiver. That's your sat input
Switches
The button on the wall plate.. If it's on you are watching the TV antenna on your roof
With it off... And teh sat receiver ON you watch Sat TV
With both it and the sat receiver off PARK CABLE.