チェンqing Huidi Aviation Equipment Co., Ltd.
July 13, 2026
Have you ever wondered what secrets lie behind the VHF radios used in every flight? Beyond routine communication, these systems hold fascinating technical details crucial for aviation safety. Here are nine essential facts that reveal the hidden workings of this vital flight tool.
The Very High Frequency (VHF) radio spectrum used in civil aviation is known as the Airband. This dedicated frequency range serves aviation communication and navigation needs, ensuring safe and orderly air traffic operations. The International Telecommunication Union (ITU) coordinates the allocation and management of these frequencies, with individual nations implementing specific protocols to prevent interference.
The lower portion of the Airband (108.000 MHz to 117.950 MHz) contains 200 channels spaced 50 kHz apart, primarily serving navigation aids (NAVAIDs). These include VOR (VHF Omnidirectional Range) stations and Instrument Landing Systems (ILS). VOR ground stations enable aircraft to determine their radial position relative to the transmitter, while ILS provides precise horizontal and vertical guidance for low-visibility approaches.
Frequencies between 108.000 MHz and 112.000 MHz serve ILS and terminal VOR stations located near airports for approach and departure procedures. The 112.000 MHz to 117.950 MHz range accommodates enroute VOR stations, with low-altitude variants covering smaller areas and high-altitude versions serving long-range navigation. These carefully calibrated systems form the backbone of safe air navigation.
The upper Airband segment (118.000 MHz to 136.975 MHz) provides 760 channels at 25 kHz spacing for voice communications. Pilots use these frequencies to coordinate with Air Traffic Control (ATC) for flight plans, position reporting, and clearance requests. While voice remains primary, emerging datalink technologies are gradually supplementing traditional radio communications to enhance efficiency.
Aviation VHF radios employ Amplitude Modulation (AM), similar to AM car radios. Despite Frequency Modulation's (FM) superior audio quality, AM persists in aviation due to historical adoption and technical advantages. AM demonstrates better interference resistance and long-range propagation characteristics, while its simpler receiver design aligns with aviation's reliability requirements.
AM systems allow stronger signals to override weaker ones, enabling ATC to interrupt aircraft transmissions when necessary. This proves critical during emergencies when controllers must immediately respond to distress calls or override stuck microphones causing continuous noise interference.
Unlike FM systems where stronger signals completely suppress weaker ones (called capture effect), AM receivers process all incoming signals simultaneously. This prevents the disruptive signal switching that can occur when multiple FM transmissions compete, ensuring more reliable communication in congested airspace.
Radio range expands dramatically with altitude due to Earth's curvature. At 4,500 feet, typical transmission range reaches about 100 miles, while at 35,000 feet it extends to approximately 200 miles. Atmospheric conditions like temperature inversions can further influence signal propagation through refraction effects.
VHF signals slightly exceed optical line-of-sight due to atmospheric refraction bending radio waves back toward Earth. This phenomenon allows communication with ground stations even when they're not visibly detectable, though pilots must account for potential signal degradation at extreme ranges.
Understanding these VHF radio characteristics helps pilots optimize communication strategies and enhances overall flight safety. As the critical link between aircraft and ground services, proficient radio operation remains an essential skill for all aviators.
