Which factors limit the effective range of VHF transmissions under normal conditions?

The effective range of Very High Frequency (VHF) transmissions is primarily influenced by two critical factors: the curvature of the Earth and the line-of-sight propagation characteristics.

As radio waves travel, they tend to follow the curvature of the Earth. This means that as the distance from the transmitting antenna increases, radio signals may not reach a receiving antenna that is beyond the horizon. The height of the transmitting and receiving antennas can mitigate this effect to some extent, but the fundamental issue remains that signals are limited by how far they can travel before they encounter the Earth's curvature.

Additionally, VHF signals primarily propagate via line-of-sight, which means the transmitting and receiving antennas must be within clear sight of each other for effective communication. Obstacles such as buildings, mountains, or even the Earth's terrain can block these signals, further limiting their range.

Therefore, the combination of the Earth's curvature, which affects how far the signal can travel before being obstructed, and the line-of-sight requirement between antennas, are the primary factors that limit the effective range of VHF transmissions under normal conditions.