Longwave frequencies refer to a range of radio frequencies that are part of the electromagnetic spectrum. Longwave radio signals have wavelengths that are longer than those of both AM (Amplitude Modulation) and FM (Frequency Modulation) radio waves. Longwave frequencies are typically associated with low-frequency radio transmission and have specific applications.
Longwave frequencies cover the range from about 30 kHz (kilohertz) to 300 kHz. They are primarily used for specific purposes due to their unique propagation characteristics, which include:
- Ground Wave Propagation: Longwave signals can propagate along the surface of the Earth, following its curvature. This makes them suitable for ground wave propagation and allows them to cover large areas with relatively low power.
- Penetration: Longwave signals can penetrate obstacles like buildings, trees, and hills, making them suitable for broadcasting in urban areas and over uneven terrain.
- Nighttime Propagation: Longwave signals are more effective during the nighttime when the D-layer of the ionosphere, which attenuates radio signals, is less active. This allows long-distance propagation.
- AM Broadcasting: Longwave frequencies are used for AM broadcasting, particularly in regions where long distances need to be covered. They are sometimes referred to as “medium wave” frequencies.
- Navigation Systems: Longwave frequencies are also used for navigation systems such as Non-Directional Beacons (NDBs), which provide navigational aid to aircraft.
- Time Signal Broadcasting: Some longwave stations are used for broadcasting accurate time signals that are used for synchronization purposes.
It’s important to note that longwave frequencies have limitations in terms of audio quality and data transmission capacity. While they are useful for certain applications, they are not well-suited for high-fidelity music or data communication. Longwave broadcasting has historical significance and remains in use for specific purposes, although advancements in technology have led to the prominence of other communication methods such as digital broadcasting and satellite communication.