I had not listened to shortwave radio broadcasts for many years, but on a whim I turned on a portable SW set a few days ago during the evening, and while tuning around I heard a loud signal with spoken Japanese.
It turned out to be an NHK World Radio broadcast. I had been familiar with NHK World (through an app and through the web). I had thought that that service was strictly limited to broadcasting in languages other than Japanese, however I was mistaken. It turns out that NHK does have a Japanese language version of that service.
The program that I listened to started off with five minutes of news, and then shifted to a series of segments that included some interviews, a weather broadcast, some story-reading or back-and-forth discussions between the hosts (some of which may have been intended for children, such as a tale about oni or yokai and demons), and more. The broadcast lasted for two hours.
The pace of the speaking was pretty rapid - I am at about an ‘advanced beginner’ level in my Japanese (around JLPT N4 level) - and I could understand a great deal of the vocabulary, although I do need to practice my listening comprehension at such a rapid conversational pace - I’m thinking that this would be a good source for practice in the future.
Due to the nature of shortwave radio broadcasting, even though it was a very strong signal, there was some fading of the signal (and I have some local powerline noise which also caused some interference). I was using a cheap portable shortwave receiver with just a short telescopic whip antenna - but I do also have more capable shortwave receiving (and transmitting) equipment and antennas which I will try using in the future (since I am a licensed amateur radio operator).
I live in the Eastern United States, and the broadcast frequency that I happened to run across was 6105 kHz (in the 49-meter band), AM. It was broadcast from 9 PM to 11 PM US Eastern time (which is from 0200 to 0400 UTC) - for those of you who may not be familiar with shortwave radio propagation, that time of night and that frequency band are not typically where I would expect to hear a shortwave signal coming directly from Japan.
After a bit of investigation I found out that the signal was being relayed from a powerful broadcast site located in France - and that they were beaming the signal for intended reception in Central America. They do, however, also broadcast from a site in Japan, on different frequencies and at different times, with intended audiences in various regions of the world. I found an official timetable here (scroll down to page 5 for the Japanese service listings):
https://www3.nhk.or.jp/nhkworld/ja/information/brochure/pdf/radio_frequency_schedule.pdf
I have not (yet, anyways) located a website or app where I can listen to the same content that they broadcast on shortwave radio, but I have not yet tried doing an exhaustive search.
(I thought that this info would deserve a thread by itself, but I may link to this thread from one of the other listening threads.)