Case No. #1512
The Unidentified Radio Signals from Iriomote's Jungle
Summary
Between 2021 and 2023, amateur radio operators and Bureau investigators on Iriomote Island in Okinawa received intermittent signals in the 40–50 MHz band from an unidentified source within the island's dense subtropical jungle. The signals followed a dot-dash pattern resembling Morse code but did not translate to any known coding system. Triangulation during a 2022 Bureau survey pointed to an inland jungle area with no known facility. Cross-checking with JASDF, Japan Coast Guard, and US military radio registries found no matching authorized transmitter.
Details
Iriomote Island, the second-largest island in Japan by area, is largely covered by subtropical old-growth forest (Iriomote-Ishigaki National Park), home to the Iriomote wildcat and other endemic species. The vast majority of the island is undeveloped. Settlements are limited to coastal areas; the deep jungle has no resident population.
The first detection, September 2021, was made by an amateur radio operator in his fifties who had set up an antenna at a high-clearance point on the island. He received patterned signals in the 40–50 MHz band with a dot-dash structure resembling Morse code. Translation produced no meaningful text in any known Morse variant. Signal strength suggested the source was on or near the island.
In 2022, Bureau investigators conducted a three-day on-site measurement session and recorded 12 signal reception events. Triangulation from multiple stations pointed to a specific inland direction — a jungle zone with no known structures or installations. Cross-checking with Japan Air Self-Defense Force, Japan Coast Guard, and US military facilities (including Kadena Air Base) found no registered transmitter corresponding to the signals.
The 40–50 MHz band properties were reviewed for natural-source possibilities, including ionospheric scatter and corona discharge. Neither typically produces the kind of regular patterned signals observed. Historical research identified several Japanese and US naval vessels sunk near Iriomote in the final months of the Pacific War; unrecovered communications equipment was noted as a theoretical possibility, though no mechanism for such equipment to maintain active transmission has been established.
Timeline
- September 2021Amateur radio operator receives patterned Morse-like signals in 40–50 MHz band from unidentified source.
- 2022 (survey)Bureau three-day measurement: 12 reception events logged. Triangulation points to inland jungle; no known facility there.
- 2022 (cross-check)JASDF, JCG, and US military radio registries queried; no registered transmitter matches.
- 2023Signal reception continues. Pattern analysis researchers attempt decoding without success.
- 2023 (historical)Wartime vessel sinking records near Iriomote surveyed; unrecovered communications equipment cited as theoretical factor.
- PresentSignal database and frequency analysis continuing.
Witness Testimony
Amateur radio operator (male, 50s)"I picked up a patterned signal in the 40–50 MHz range. Short and long pulses, like Morse. But translating it produced nothing meaningful. The strength implied a nearby source, but nothing should be there."
Bureau investigator (male, 40s)"Twelve reception events in three days. Triangulation pointed toward the island's jungle interior. No facility in that direction. JASDF, Coast Guard, and US military — no registered match."
Communications researcher (male, 50s)"A regular patterned signal from a natural source is not normal. There is an artificial transmitter somewhere. Where exactly is unknown. Wartime equipment being active is unlikely but not zero as a possibility."
Kyu's Analysis
A signal with a pattern comes from the jungle. Triangulation confirms the direction. Nothing is registered there. Iriomote's jungle is transmitting something.
