Advanced tone-generator morse training gear for a group operation. It allows up to 4 individual training posts, or one two participant connection with other two individually trainig, or two two participant connection, or full four participants net traffic. Slightly "rough" tone, because of square wave.
Made by VOP-064 in CZ, Hradec Králové. VOP is the abbreviation of "Vojenký opravárenský podnik", which means "Military service facility".