Periodic spectral signal — a technosignature class consisting of a train of narrowband pulses (sub-FM-channel bandwidth, periodic temporal structure). Distinct from:
- Classical CW narrowband beacons — continuous emission at a single frequency.
- Pulsars — naturally periodic but broadband.
- Fast radio bursts — singular or stochastic, generally broadband.
- Broadband leakage signatures — terrestrial-style civilization radio leakage.
Rationale
A train of pulses is more energy-efficient for interstellar communication than continuous emission (vishal-gajjar, src-seti-galactic-center-search-2025-07). The combination of narrow bandwidth + periodic temporal structure is the discriminator from natural astrophysical sources (steve-croft).
Vault searches
- BLIPSS — first comprehensive search optimized for this signal class; 4–8 GHz Galactic Center target on the Green Bank Telescope (src-seti-galactic-center-search-2025-07).