FM or frequency modulation is a mean of modulating carrier with information or base signal in radio technology so that the RF or radio frequency can be propagated to distance receiver from a transmitter. There are three basic methods of modulation for radio frequency. They are CW or continuous wave, AM or amplitude modulation and FM or frequency modulation. CW or continuous wave was used in older days for Morse code transmission in the way that a fixed frequency and fixed amplitude signal wave was switched on and off and transmitted. this on and off signal was carrying Morse code information to the other side of receiver. In amplitude modulation a fixed frequency wave is used whose amplitude is varied according to the base frequency or information. Or in other words the base information is overlay of the carrier frequency signal. The next type is FM or frequency modulation in which the amplitude of the carrier signal is kept fixed and the base information is used to change the frequency of the carrier signal to take the information.
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| Different methods of modulation |
The time of CW had passed. There in no more use of Morse anywhere. But still the amplitude modulation and frequency modulation is in use. Amplitude modulation are affected much from external disturbances where the FM or frequency modulation is affected very less. This is the reason we hear very clear ad beautiful music and voice at FM whereas at AM band this is not possible. The other reason for clarity is the frequency modulated signal provides much wider band for modulation of base signal or information which is up to 75Khz whereas the AM or amplitude modulation provides only 5Khz of bandwidth. Modren days FM or frequency modulation signal can even modulate stereo audio signal as base frequency which can be received by a stereo receiver are receiving end. Sure stereo audio signal is way better and natural compared to mono audio signal.
Frequency modulation can also use the concept of pre-emphasis and de-emphasis. In this system the FM signal is much more amplified at transmitting end and is then attenuated with the same ratio at receiving end. In this method the unwanted signals injection is also reduced and we receive a very clear signal at receiving end.
Modern days FM receivers are using one single chip IC which is responsible for doing all the required tasks and functions. Receivers are comparatively simple for FM. FM is using high frequency band and that frequency the need of the antenna is less. A small size antenna can effectively transmit and can receive the signal. One disadvantage of FM is the signal is highly direction or it uses line of sight. In normal conditions the transmission limit is 25Km circle for an FM signal.
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