I work at a local small airport (very small, if we get more than about 10 or 15 airplanes taking off/landing it's a "busy day") and I mow the runways (we have multiple grass ones).
Because of the visual obstructions of the tractor's cabin that I use I have to be even more careful than normal to check for in-coming planes and so I started looking into getting an air band radio for the tractor. However, they can be fairly expensive - not something I'd invest in unless I absolutely had to - and so I started looking into making my own.
I'd figured this was possible because I'd occasionally picked up communications on a cheap radio I had around my house (I live quite close to the airport, about a 5 minute bike ride). So, I went searching, and sure enough - this is a thing that is possible and has been done.
I found this post on Electrical Engineering.SE, Modify an AM/FM radio to an airband receiver, describing basically what could be done; and then this video done by MAKE, Weekend Project: Aircraft Band Receiver, showing it actually being done to cheap transistor radio.
Now, what I'm wondering is, is this a legal thing to do - or does the FAA have regulations on this sort of thing?