Searching for Interstellar Sawtooth Noise: A Viable Approach for SETI Investigators

Would it make sense for SETI (Search for Extraterrestrial Intelligence) investigators to look for the “sawtooth” noise signature of channelized communications systems such as the standardized TV channelization and spacing on Earth? This is an intriguing question considering the complexity and challenges involved in detecting such signals over vast interstellar distances.

Potential Challenges and Considerations

One might initially think that TV-broadcast radio waves would be far too weak to be detected at multi-light-year distances. However, the difficulty in receiving signals even at short distances on Earth underscores the significant technological hurdles involved. Additionally, television broadcasting channels are not uniformly spaced as one might expect. Each channel occupies a frequency band centered on a carrier frequency, with neighboring channels typically separated by 6 MHz. The television broadcast frequencies are as follows:

Nevertheless, ETI (Extraterrestrial Intelligence) broadcasts may follow different frequency conventions, making it challenging to identify where to look. Therefore, it is essential to scan a broad range of frequencies to increase the chances of detection. The interstellar communication environment presents unique challenges, including a substantial galactic background that is broadband with some spectral lines. To mitigate the galactic background, narrowband detection methods are often employed, focusing on signals with bandwidths as narrow as 1 Hz or less.

Channelized Communication and Narrowband Signals

TV broadcasts include carrier waves with much of their signal power concentrated in narrowband parts of the spectrum. This characteristic makes the carrier waves more detectable over interstellar distances using narrowband receivers. However, receiving a complete TV broadcast over such distances would be extremely difficult without utilizing a planet-sized telescope. This factor significantly complicates the feasibility of watching Earth's TV shows from exoplanets.

Efficient Signal Transmission: Compression and Timing Pulses

Given the challenges, it is likely that any ETI would employ compression techniques similar to those used on Earth. As a result, the primary signal of interest would be the timing pulses used to send data packets. This approach aligns with efficient communication practices that minimize energy usage and maximize bandwidth utilization. Additionally, it is safe to assume that any ETI would reside in a solar system with an accretion disk and would have developed planetary defense systems, which could provide their strongest detectable signals in both the optical and radio ranges.

Conclusion

While the detection of “sawtooth” noise from channelized communications like Earth's television broadcasts remains challenging, it is not entirely without merit. Combining the search for narrowband signals with a thorough frequency scan and focusing on timing pulses for data packets could provide a fruitful approach for SETI investigators. As technology advances, the possibility of detecting such signals in the future may become more realistic.