According to the book The Aquariams of Pyongyang, Chinese -made wirelesses are available in Pyongyang. I have also learned that such wirelesses are smuggled in across the border (from China). I could imagine that shortwave would not be of much use in DPRK since most everybody only speaks Korean. K.B.S. in South Korea transmits medium-wave from sites not far from the D.M.Z. at very high powers and no doubt that's how those in the North can hear broadcasts from outside the country. Of course, the penalties for listening to such transmissions are incredibly harsh. By the way, I spent two hours listening to wireless stations from the DPRK tonight.
I was thinking that those homemade rx's are probably MW. MW rx's can be pretty simple-anybody remember the "boy's radios" of the 50s that were two or three transistors in what was probably a regenerative circuit?