The frequency range of 30 to 300 MHz that is defined as VHF does not normally support any other propagation modes than ground or surface waves. These are limited to line-of-sight and sligthly beyond using “reasonable” antenna sizes and power levels.
Do VHF radios work by line-of-sight?
VHF radio waves propagate mainly by line-of-sight, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 km (100 miles).
Is VHF line-of-sight only?
Some are based on the distance to the horizon and some for the radio horizon. Remember, VHF is considered to be line of sight radio, although in most cases there is some bending of the radio waves however slight.
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”.
What are the limitations of VHF transmission?
Their range is further limited by their inability to pass through hills or large structures. Accordingly, VHF waves are limited to use in short-range, line-of-sight communications, including radio and television broadcasting, and in electronic navigation systems.
Is FM a line-of-sight?
Line of sight (LoS) is a type of propagation that can transmit and receive data only where transmit and receive stations are in view of each other without any sort of an obstacle between them. FM radio, microwave and satellite transmission are examples of line-of-sight communication.
How far can 400 MHz reach?
Thus the typical ranges with around 400 MHz frequency range with 1 W transmitter power are up to ~30 kilometers and up to ~80 kilometers with 10 W transmitter power.
What VHF channel should I use?
Federal Communications Commission regulations require boaters having VHF radios to maintain a watch on either channel 9 or channel 16, whenever the radio is turned on and not communicating with another station. All non-emergency traffic should be communicated on another channel (not channels 9 or 16).
Why do microwave antennas need line-of-sight LOS communication?
Because of the high frequencies used, a line-of-sight path between the stations is required. Additionally, in order to avoid attenuation of the beam, an area around the beam called the first Fresnel zone must be free from obstacles. Obstacles in the signal field cause unwanted attenuation.
What is the range of VHF and UHF?
Car, Boat, & Other Radios (Mobile & Fixed-Mount)
|Average Range Guidelines *|
|Wattage||Flat Open Terrain (miles)||Urban Areas (miles)|
|4 watts (UHF)||4 – 6||1½ – 3|
|5 watts (VHF)||4½ – 6||1½ – 2|
|12 watt CB SSB (HF)||8 – 15||3 – 5|