The problem with using the DB20-G to build a repeater is what is called “Duty Cycle.” In the design and engineering of a transciever they decide the average time that the unit will be in “transmit” (especially on HIGH power) as compared to “receive” and then using this percentage they design the needed heat sinks to to disapate the heat away from the chips generating the heat.
The DB20-G, like most transceivers at this price range, will get extraordinarily hot when left on transmit on HIGH for long periods of time and of course, by its very nature, the radio used in a repeater to retransmit received transmission will be on transmit for a much longer period of time that was designed and engineered into the radio.