I recently purchased a pallet (!) of Mastr III repeaters for some parts. These are really unique radio systems since they're so modular, so I thought you'd enjoy a video where I tear one apart and talk through its basic theory of operation.
I mention the video I've previously done on phase locked loops.
Repeater Builder has a prohibitive amount of information on the Mastr line of radio, including a giant list of datasheets on each module which I really enjoy.