A radio communication in Morse code and amateur radio terminology!

Here's a breakdown of the message:

* `00:46 JR4ARN/P`: The time is 12:46 AM (in 24-hour format), and the call sign is `JR4ARN/P`, which indicates that the station is operated by JR4ARN, a Japanese amateur radio operator with a permission to operate on the higher power limit (indicated by `/P`).

* `on JP-0023`: The station is located in or near Setonaikai National Park, and the QTH locator (`JP-`) indicates that it's somewhere on the island of Honshu.

* `(Setonaikai National Park, ...)` : A list of nearby park locators (i.e., geographic areas) mentioned in parentheses, including:

+ JP-EH: Ehime Prefecture

+ JP-FO: Fukuoka Prefecture

+ JP-HG: Hiroshima Prefecture

+ JP-HS: Hyogo Prefecture

+ JP-KG: Kagawa Prefecture

+ JP-OS: Okayama Prefecture

+ JP-OT: Oita Prefecture

+ JP-OY: Osaka Prefecture

+ JP-TS: Tokushima Prefecture

+ JP-WK: Wakayama Prefecture

+ JP-YC: Yamanashi Prefecture

* `21074.0 FT8 QRT`: The station is operating on the frequency 21074.0 kHz, and using the mode FT8 (a digital mode). The message indicates that the operator will go Quiet (QRT) soon.

* `TNX QSO QSY [JR4ARN]`: The message thanks all participants for their QSOs (communications) and announces a frequency change (`QSY`).

In summary, JR4ARN is an amateur radio operator operating on FT8 mode from the Setonaikai National Park area, and will soon be going quiet.