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Radio Wave Propagation – Very High Frequency (VHF) Radio
VHF is the 30–300 MHz band, with wavelengths from about 10 m to 1 m. Compared with lower frequencies, these shorter wavelengths travel mainly as direct space-wave (line-of-sight) signals.
That means VHF does not normally bend around the Earth enough to give long-range surface-following coverage like LF ground wave.
In practice, this is why VHF is used heavily for aviation communications: the signal is generally clear, stable, and less affected by the static/noise that is common on lower-frequency bands. The mention of squelch is important here — squelch mutes background receiver noise when no valid signal is being received, so you only hear usable transmissions.
In the picture, the transmitting antenna radiates in many directions, but useful reception depends on whether the aircraft is still in line-of-sight of the transmitter.
The aircraft on the near side of terrain/curvature is marked Radio Reception.
The aircraft beyond the terrain/curvature shadow is marked No Radio Reception.
So the limitation is not that the transmitter stops radiating — the limitation is geometric line-of-sight between transmitter and receiver.
Key Points
VHF band: 30–300 MHz.
Wavelength range: 10 m to 1 m.
Main propagation mode: line-of-sight (space-wave).
Main operational use: clear, reliable communications with less static than lower frequencies.
Squelch reduces background noise when no valid signal is present.
Terrain and Earth curvature can block VHF, creating reception “shadow” areas.
Near aircraft may receive clearly while farther aircraft may receive nothing due to line-of-sight limits.