It's better to bypass the RV External TV Jack to prevent interference for the satellite antenna. You need a direct path from the dish to the receiver for best results.
The Dish antenna cable screws on to the connection at the back of your receiver box marked as "Satellite Antenna In" or something similar. Then you connect a cable from the receiver box connection marked "Out To TV" or "TV Out" to your TV Or use the RCA connectors (Red,Yellow & White) or HDMI cable if so equipped to get the signal from the receiver to the TV.