Hinckley Radio Control Car Club

I was wondering if any one could explain, or could give me a link to an in depth explanation of how the transponder system like we use at Hinckley actually works.
I've had a look on google which just gave me a vague idea. Found a couple of images where someone had removed the top off a transponder, but I couldn't really make out exactly what was in it.

Any info?

regards
Ian

Roger may be the man to talk to. He knew a lot about it when I spoke to him.

I've only got theories on how they work rather than facts!