The maximum distance a line-of-sight microwave transmitter can span without repeaters depends on several factors, including the frequency used, antenna height, transmitter power, atmospheric conditions, and terrain. Here are some general considerations:
Frequency: Higher frequency microwaves (e.g., 30 GHz) generally have shorter ranges compared to lower frequency microwaves (e.g., 6 GHz). Higher frequencies are more susceptible to attenuation caused by atmospheric moisture and other obstacles.
Antenna height and gain: The height of the transmitting and receiving antennas plays a crucial role. Increasing the height can extend the line-of-sight range by reducing the impact of obstacles such as buildings, hills, and vegetation. Higher gain antennas can also improve the range by focusing the signal more effectively.
Transmitter power: Higher transmitter power can compensate for some signal losses and increase the range. However, there may be regulatory limitations on the maximum allowed transmitter power.
Atmospheric conditions: Atmospheric factors such as rain, fog, and atmospheric turbulence can attenuate microwave signals, reducing the range. Adverse weather conditions may require additional power or signal processing to maintain reliable communication.
Terrain: The terrain between the transmitter and receiver can affect the line-of-sight range. Flat terrain generally allows for longer distances compared to areas with hills, mountains, or dense vegetation that can block or scatter the signal.
In ideal conditions, with appropriate equipment and favorable factors, line-of-sight microwave links can span tens of kilometers (20-50 km or more) without repeaters. However, it's essential to conduct a detailed site survey and consider all the aforementioned factors to accurately determine the achievable range for a specific microwave link.
Keep in mind that for longer distances, repeaters or relay stations are often necessary to amplify and regenerate the signal to maintain reliable communication over extended distances or when there are obstacles in the line of sight.