From sigidwiki: "The Japanese Slot Machine (Enigma Designation XSL) is a simplex system used by the Japanese Maritime Self-Defense Force in Ichihara, Japan.Uses QPSK at 1500 Bd to transmit. Has a very interesting and unique idling format which sounds akin to a slot machine, hence the attributed name. This modem has been active since 2001." Recorded while at "idle" before any data is streamed, Sedona WebSDR, April 25, 2021. 6251.9 kHz.