Longwaves

Longwaves, also known as very low frequency (VLF) radio waves, are a type of radio wave with wavelengths ranging from 1 kilometer to 10 kilometers. This corresponds to frequencies from 30 kilohertz (kHz) to 300 kilohertz (kHz). In the broader electromagnetic spectrum, longwaves fall between very low frequency (VLF) and low frequency (LF) bands. Historically, they were used for long-distance broadcasting and telegraphy before the widespread adoption of shorter wavelengths. Their ability to travel long distances and penetrate obstacles like mountains and water has led to their continued use in specific applications.

The propagation of longwaves is characterized by their groundwave component, which follows the curvature of the Earth, and their skywave component, which is reflected by the ionosphere. This dual propagation mode allows for reliable communication over vast distances, even during the day when skywave propagation can be attenuated at higher frequencies. However, longwaves are susceptible to atmospheric noise, particularly from lightning discharges, which can limit their use in certain environments or for highly sensitive applications.

Modern uses of longwaves include time signal broadcasting, navigation systems like LORAN (though largely superseded), submarine communication, and some specialized broadcasting services. The relatively narrow bandwidth available in the longwave spectrum limits the amount of information that can be transmitted, making them unsuitable for high-fidelity audio or data transmission compared to higher frequency bands. Despite these limitations, their unique propagation characteristics ensure their continued relevance for niche communication needs.