I recently purchased an old receiver from the 1940s, someone who had previously had it had painted the front blue and added labels with his name and callsign. He puts his call as WDX7CYJ. I have never heard of a 3x3 callsign ever... Not it America or anywhere else. Does anyone know anything about these kinds of calls? When they were given out or where? The name on it is Ben Almojuela, so I was maybe thinking it was maybe a Mexican call.