How Radio Frequencies Allow Pilots to Communicate

Have you ever wondered how pilots can maneuver through the sky without crashing into each other? It’s mainly due to communications antennas. Aircraft use radio frequencies to navigate and communicate with air traffic control.  Each antenna has different frequencies and applications which determine where on the aircraft they are located. 

When communicating with air traffic control (ATC), these antennas are operating short-range using a very high frequency (VHF) band between 118 MHz and 137 MHz. Since the aircraft is constantly moving, the signal must be sent in all directions to ensure it is received.  These VHF frequencies operate with line-of-sight capabilities, meaning that the range only reaches the visible horizon.  The height of the antenna being used determines what kind of range you get–higher antenna means wider range. 

These antennas can be found either on top of the aircraft or underneath it. They are slightly bent and usually made from white or stainless steel.  The standing wave ratio (SWR) for these should typically be between 1:1 and 1:2; this refers to how well the antenna performs and how much of a reflection is coming off the antenna.  Antennas like these must be grounded well, meaning that they need a strong mounting sheet that will reflect the signal back toward the transmitter.

Since VHF is only recommended for short distances, the high frequency (HF) band is used for long-range communication needs.  Airliners are equipped with satellites that allow them to have long-range communications while they travel, and to provide accommodations like wireless internet to their passengers. These airliners are supplied with special radios and a vertical antenna that work with the HF band to take over communication once they leave the range of the VHF.


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