The Sojourner rover was deployed as part of the Mars Pathfinder mission. At the end of the mission, the Sojourner rover was still operable. But the base station that the Mars Pathfinder carried failed. So communication with the rover was lost. Presumably the base station is completely inoperable after this failure.
I can't find any specifications on the frequency used to communicate from the base station to the rover. But the rover has a prominent dipole antenna sticking out of it. This is presumably it's only radio antenna. Is the rover just sitting there waiting for its next set of commands? If I had the correct antenna and transmitter in orbit around Mars, could I start using the Sojourner rover again?