Communication in ATC

Communication is the two way process of exchanging information in which English is widely used. Here the intelligence which is the data is being exchanged between the ATC and the pilots through RF bands. Mainly for communication transmitters , receivers and oscillators are used for generating , transmitting and receiving radio freq signals .
The RF bands used in air craft communication are
*. HF ranging from 1.6 MHZ to 30MHZ
*. VHF ranging from 300MHZ to 3000MHZ
The main advantage of VHF over HF is it is less noisy. This is really very useful in the part of pilot since it does not affect his ears. But its main disadvantage is it is meant for short range communication. So when the plane moves out of the range , HF communication is used . Generally HF is used when the plane travels over the oceanic region . The main disadvantage in HF is noisy . since it is noisy the pilots cannot wear the head phone continuosly , So inorder to communicate the information from the base station to the pilot a new method called SELECTIVE CALLING is used. In this method a four letter code is generated from the base station which shows an indication to the pilot in the form of a beep.Once he gets the beep he use the head phones and the message is passed to him.