Each system comprises a transmitter which consists of a current source, producing an alternating desired frequency of oscillation. The transmitter contains a system for modulating (selecting) certain goods of the generated energy to print a sign on it. This modulation can be as simple as transforming energy or modifying more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter transmits the modulated electrical energy to a tuned resonant antenna; This structure converts the fast-moving alternating current into an electromagnetic wave that can move through the free space (sometimes with a particular polarization).
Amplitude modulation of a carrier wave operates by varying the intensity of the transmitted signal in proportion to the transmitted information. For example, changes in signal strength can be used to reflect the sounds must be reproduced by a speaker, or to specify the brightness of the television pixels. It was the method used for the first transmissions of audio radio, and is still used today. “AM” is often used to designate the half-wave band (see AM radio), but it is used in various radiotelephony services such as Citizen Band, radio ham and especially in aviation, due to Of its ability to be received under very low signal conditions and its immunity to capture the effect, allowing you to hear more than one signal simultaneously.
The frequency modulation varies the carrier frequency. The instantaneous carrier frequency is directly proportional to the instantaneous value of the input signal. FM has the “capture” effect by which a receiver receives the strongest signal even when the others are present. The digital data can be sent by changing the frequency of the carrier from a set of discrete values, a technique known as frequency shift. FM is commonly used at very high frequency (VHF) radio frequencies for the transmission of high fidelity music and speech (see FM broadcasting). The analog TV sound is also output with FM.
Angle modulation modifies the instantaneous phase of the carrier wave to transmit a signal. It can be FM or phase modulation (PM).