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. In this article, we will discuss common difference between AM and FM which will enhance our learning in terms of these two technologies.
1. Evolution: Formulated in the 1870s, AM is a relatively older modulation process compared to FM which was found in the 1930s by Edwin Armstrong.
2. Technology: AM stands for amplitude modulation where the 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.
3. Frequency range of working: Amplitude modulation works between 540-1650 KHz while FM works at 88-108MHz.
4. Power Consumption: FM based signal transmission consumes a higher amount of power than an equivalent AM based signal transmission system.
All Metro and most Tier-2 Cities have their own commercial channels that work on FM
5. 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.
In pre-emphasis, de-emphasis process, the signal is further amplified to a higher frequency at sending end (pre-emphasis) and vice versa at receiver end (de-emphasis). These two processes reduce down the chances of a signal to get mixed with other signals and make FM more immune to noise than AM.
6. 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.
7. 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.
8. Bandwidth consumption: AM signals consume 30KHz of bandwidth for each while in FM 80KHz 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.
9. 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.
10. Commercial Aspects: Setting up an AM based radio communication system is very economic as there is no complicated circuitry and processes are easy to understand.
A few radios come with AM and FM functionality
On the other hand, FM is a fairly complicated communication system and requires high capital investment and expertise at work. Commercially FM based radio systems are more popular due to high signal quality (especially audio) and more immunity to noise.