In March 1971, days after the Calder Ridge array came online, the station recorded a narrow-band signal near 18.633 kilohertz. It was assumed to be a fault in the new instrument. It was not. When the instrument was replaced, the signal remained; when a second, independent receiver was installed, it recorded the same thing.
In the decades since, FA-0447 has returned intermittently, always at the same frequency, held to within a fraction of a hertz. It does not track any catalogued transmitter. It does not follow any satellite pass. It shows no periodicity that matches a celestial or orbital cycle. Its returns can be described with precision and predicted with none.
The Laboratories carry FA-0447 as their longest-standing unresolved entry. No claim is made as to its origin. The honest description is the one given here: a clean, stable, recurring signal, from a source we have not been able to identify, that has outlasted most of the people who first recorded it.
What the public record includes
First station log
Carrier appears during commissioning and is initially treated as instrument fault.
Independent receiver check
Replacement receiver records the same narrow-band feature within the public frequency tolerance.
Transmitter review
External frequency-use review finds no licensed or scheduled source that accounts for the returns.
Modern recurrence review
Retained as Class III after updated false-alarm and maintenance crosswalk review.
Review method
- Narrow-band extraction around the public center frequency.
- Receiver-lineage comparison across hardware generations.
- Station downtime removal before recurrence analysis.
- Sidereal, seasonal, and orbital period checks.
Ordinary sources checked
- receiver self-oscillation
- licensed fixed transmitter
- satellite pass
- maintenance schedule artifact
- Exact receiver geometry and station-bearing material are not public.
- The public record does not identify a source.
- New returns remain manual-review events until released by the review office.