I'm going to give you generic answers. These RVs can be quite frustrating.
1. As mentioned above, you have a antenna booster amplifier with a tiny switch. There is usually a tiny led light next to the switch. Usually located next to or beside the radio/TV area. Maybe inside a cabinet next to that area. Mine is hidden next to the 12volt DC plug near TV. Hard too see.
2. You should have an antenna! It may be a new Omni directional unit that looks like a mushroom.... Instead of the normal antenna that raises.
3. The radio and TV share the same antenna. So the amplifier provides gain to both units.
If you don't have a TV installed, find the antenna connection and trace that wire back until you find the junction where it joins the radio antenna. Should be a box there with a splitter.
The box should be powered...trace that back until you find the switch.
4. The only other thing that comes to mind is assuming this is a used RV, did the previous owner remove the antenna? Was there roof damage and the antenna wasn't replaced after repair?
5. I guess an RV could come without a radio and antenna. But I've never seen one.
So start the process of investigating your rig. Yes you will need to take things apart to trace wires. Just take your time, take pictures to help putting things back together.
One word of caution, my trailer radio wires were a mess! And the manufacturer used the cheapest wire connectors. Thankfully, I took pictures so when some of the wires came apart, I was able to put them back together. Very poor workmanship when built!
The upside to this work is this will help you understand how your RV is built. Believe me, any experience you get from digging into your RV will be beneficial later on!
2015 Sierra 1500 Denali
2014 Coleman 249RB
David Jon Devoucoux
People, Places & Things...for over 40 Years!