From 1994 - 2003 every manufacturer designed their own DIRECTV receivers from the ground up. But when News Corp took over their vision was a standard user interface and remote control for every box, so customers and their CSR could more easily support the products.
So LG, Philips, Samsung, Thomson and Humax all build the same box to DIRECTV's specifications.
100=RCA/Thompson
200=Samsung
300=Phillips
400=Hughes
500=Humax
600=LG
so your H-20-600 would be mfg. by LG.