Copyright definitely exists long after the creator's death, and is automatically assigned. So schematics, documentation, etc. would all be covered by copyright protection.
I don't know much about patents, other than they're different, they have to be applied for, and meant to deal with specific inventions to ensure that the inventor(s) receives the benefits of their work. Here is a link that describes them pretty well from a Canadian perspective: Patents.
So you couldn't patent generic circuits in a schematic, as an example, but you can patent a specific implementation of, say, a VFO if it's innovative and different. I don't know whether anything in the SSTRAN transmitters, or the transmitters themselves, was/were patented.
But the schematics and other documentation certainly are under copyright protection. And if they're being published on github, or included in whatever the DT6000 guys send you when you purchase their vaporware, that would be a copyright violation.
I also think it's rather amusing that they're apparently ripping off the SSTran (which has been the target of nothing but derision by the guys over at the other Forum), modifying it, they claim, for the better, but they want to patent one of their modifications. I guess the patent office will decide how innovative and different that modification really is.