My two cents in addition to lebuffon's reply: The occasional amateur gear is usually not enough to demodulate signals from Mars, since they're too faint. You'd

My two cents in addition to lebuffon's reply: The occasional amateur gear is usually not enough to demodulate signals from Mars, since they're too faint. You'd need much larger dishes to, roughly speaking, "ingest" more energy into your receiver so that it become more distinguishable from noise and you can extract information from it. It would be possible to demodulate with smaller, amateur dishes if the spacecraft transmitted in a very narrow bandwidth. It wouldn't make sense for space agencies to do that, though, since they would trade higher bit rates for cheaper receivers, whilst powerful receivers aren't that difficult to build and are totally on budget for an agency capable of launching a spacecraft. But I must say that that would be a very nice citizen science project.