Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM)

       AM, FM and PM.
       In radio communication, the message signal wave (low frequency) is combined with a carrier signal (high frequency). In this combination, one or more characteristics of the carrier wave are varied with respect to message signal. This variation is termed as modulation and it is needed so that message can be transmitted over long distances and no undesired signal mixing takes place.

                              

•      Depending on several factors such as range, application and budget, modulation can be casted into three types: Amplitude Modulation, Frequency Modulation and Phase Modulation. Out of these three types, the former two are widely known as they form a major commercially applicative part of radio communication

•      Frequency range of working: Amplitude modulation works between 540-1650 KHz while FM works at 88-108MHz. 

•      Power Consumption: FM based signal transmission consumes a higher amount of power than an equivalent AM based signal transmission system.

AM vs FM: 

•      Signal Quality: Signal quality is a lot superior in FM than AM as amplitude based signals are more susceptible to noise than those which use frequency.  Moreover, noise signals are difficult to filter out in AM reception whereas FM receivers easily filter out noise using the capture effect and pre-emphasis, de-emphasis effects. In capture effect, the receiver locks itself to catch stronger signal so that signals received are more synced with that at the transmitting end.

•      Fading: Fading refers to power variation during signal transmission. Due to fading, the power with the signal received can vary significantly and reception wouldn’t be of a good quality.

•      Fading is more prominent in amplitude modulation as compared to frequency modulation. That is why, AM radio channels often face the problem where sound intensity varies while FM radio channels have constant good reception

•      Wavelength Difference between AM and FM: AM waves work in the range of KHz while in FM waves work in MHz range. As a result, AM waves have a higher wavelength than the FM ones. A higher wavelength increases the range of AM signals as compared to FM which have a limited area of coverage.

•      Technology: AM stands for amplitude modulation where the a1. Evolution: Formulated in the 1870s, AM is a relatively older modulation process compared to FM which was found in the 1930s by Edwin Armstrong.
 

•      Amplitude of the carrier is modulated as per the message signal. The other aspects of the carrier wave such as frequency phase etc. remain constant. On the other hand, FM means frequency modulation and in it only frequency of the carrier wave changes while amplitude, phase etc. remain constant.

•      Bandwidth consumption: AM signals consume 30KHz of bandwidth for each while in FM 80MHz is the bandwidth consumed by each signal. Hence, over a limited range of bandwidth, more number of signals can be sent in AM than FM.

•      Circuit Complexity: Aforesaid, Amplitude Modulation is an older process and has a very simple circuitry. On the other hand, frequency modulation requires a complicated circuitry for transmission and reception of signal. The signals sent in FM are more modulated and emphasized at the transmitter and they are thoroughly checked and corrected at the receiving end. This is why circuitry for FM signals is very complicated.