Look for an antenna wall plate that looks like this...

There is a BLACK PUSH BUTTON on it that needs to be pressed and a small led green light should come on. This will provide 12VDC to the booster amplifier that is up inside the antenna...
You also should goto the menu of your HDTV monitor and select "ANTENNA" instead of "CABLE". Then you will have to point the antenna towards the town that is transmitting the NATL BROADCAST digital TV SIGNALS and scan them into the HDTV monitor just like you do at home.
You will have to do these routines everytime you stop at a new camp site.
NOTE: These are the general instructions for using the BATWING and JACK HDTV antennas. I have no idea what a mushroom antenna is...
Roy Ken