Send for a receiver if you want to hook the third TV up as a separate TV for viewing. If you just want to watch the same program on another TV, you will not need the third receiver.
Run the coax from the satellite dish to the third TV and attach the coax to the receivers input. If you are using a shared receiver, run the coax from the base receiver by way of a splitter to the third TV and connect to the TV input. You need a splitter box with an input and an output to run the extra coax.
Connect the coax to the receiver input and the short coax to the output on the receiver box and to the input of the TV. Set the TV to Channel 3.
Check the satellite signal by pressing the "Action" button and then the "Guide" button on the remote. This will take you to a screen that has a selection for set up. Click the "Set Up" button. This will take you to a screen with installation on the screen. Click on "Installation." This takes you to the screen where the signal strength is measured. Make sure you have a signal strength of 80-plus.
Keep in mind that Lost signals may be due to movement on the dish when hooking up the coax. Check the other receivers to see what the siglal is that they are receiving. If the signal is lost, you will have to position the dish correctly. See the eHow article "How to Point a Satellite Dish" if you are unsure how to do it.