In 1984 in Seoul, I managed to pick up two NHK domestic outlets on shortwave. NHK Kumamoto 6130 kHz (JKQ21) sent nice handwritten letter for a report of their transmission. NHK in Tokyo responded with a Radio Japan QSL card for a report of NHK Hiroshima 6175 kHz (JKG21). They put out fair signals into Seoul and were quite readable.
I am not sure but I believe these were links from the key stations to their subordinate stations.
Earlier this week, this verification of WQFG989 operated by the Hudson County Office of Emergency Management arrived in our mailbox. The station was mostly in the clear on 1710 kHz so it might be possible to hear it on the West Coast of North America, or at a high latitude listening post in Europe. Thank you to Coordinator Jim Woods for taking the time to type up and send this letter.