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Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations?
VHF and UHF can bend somewhat around the curvature of the Earth and thus travel further than we can see. This assumes that there are not other significant obstacles that may block the signal such as buildings, trees and hills.
Is VHF limited to line of sight?
Weak Signal VHF They generally use large directional antennas, low noise preamps and RF power amplifiers to improve their station’s performance. So VHF is not limited to line-of-sight propagation…the signals go much further.
Why is VHF propagation considered line of sight?
Therefore, since the ability to visually see a transmitting antenna (disregarding the limitations of the eye’s resolution) roughly corresponds to the ability to receive a radio signal from it, the propagation characteristic at these frequencies is called “line-of-sight”.
Is UHF line of sight?
UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz.
What mode is responsible for allowing over the horizon VHF and UHF communications?
Sky-wave propagation
Sky-wave propagation is responsible for most long-range, over the horizon communication.
How does beyond line-of-sight work?
Beyond line-of-sight (BLOS) is a related term often used in the military to describe radio communications capabilities that link personnel or systems too distant or too fully obscured by terrain for LOS communications.
Do UHF channels still exist?
UHF generally had less clear signals, and for some markets, became the home of smaller broadcasters who were not willing to bid on the more coveted VHF allocations. These issues are greatly reduced with digital television, and today most over-the-air broadcasts take place on UHF, while VHF channels are being retired.
What do you mean by line of sight in VHF radio?
The usual description of line-of-sight VHF is that the radio waves travel a bit further than the optical horizon (say 15% more) . Let’s refer to this as the Line-of-Sight (LOS) region where signals are usually direct and strong.
What do you mean by line of sight?
Let’s refer to this as the Line-of-Sight (LOS) region where signals are usually direct and strong. What is often overlooked is that beyond the radio horizon, these signals continue to propagate but with reduced signal level.
How many miles can a weak VHF signal work?
A well-equipped weak-signal VHF station in “flatland geography” can work over 250 miles on a regular basis…no exotic propagation required. Now you might think that FM behaves differently, because of the threshold effect.
What’s the difference between HF and VHF propagation?
When we teach our Technician License class, we normally differentiate between HF and VHF propagation by saying that HF often exhibits skywave propagation but VHF is normally line-of-sight. For the beginner to ham radio, this is a reasonable model for understanding the basics of radio propagation.