On this page, we will learn about the following:. Difference between AM and FM. Comparison between AM and FM. Difference between FM and PM modulation in tabular form. Distinguish between amplitude modulation and frequency modulation. AM versus FM. Amplitude modulation. Frequency modulation. Full form. AM method of audio transmission was successfully carried out in the mids. Modulating differences. In AM, a radio wave is known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted.
Constant parameters. The frequency and phase remain the same. The amplitude and phase remain the same. AM has poorer sound quality, and a lower bandwidth but is cheaper and can be transmitted over long distances as it has a lower bandwidth that is why it can hold more stations available in any frequency range.
FM is less affected by interference, but FM signals are impacted by physical barriers. They have a better sound quality due to higher bandwidth. Frequency range. AM radio ranges from to kHz or up to bits per second. FM radio ranges in a higher spectrum from Bandwidth BW. BW is much less than FM. BW is large. Hence a wide channel is required. Bandwidth requirements. Bandwidth requirement is twice the highest modulating frequency. In AM radio broadcasting, if the modulating signal has a bandwidth of 15 kHz, then the bandwidth of an amplitude-modulated signal is 30 kHz.
Bandwidth requirement is greater and depends upon the modulating. Bandwidth requirement is twice the sum of the modulating signal frequency and the frequency deviation. No of Sidebands. The number of sidebands are constant and equal to 2. The number of sidebands having significant amplitude depends upon the modulation index.
Zero crossings in modulating signal. Not equidistant. FM or PM transmitters are more complex than AM because the variation of modulating signal has to be converted and detected from the corresponding variation in frequencies. AM receivers are very less susceptible to noise because noise affects the amplitude, which is where information is stored in AM signals. FM receivers are better immune to noise and it is possible to decrease noise by further deviation.
Power is wasted in transmitting the carrier. Wideband FM was invented to specifically overcome the interference disadvantage of AM radio. The disadvantage of FM signal is that it is more local and cannot be transmitted over long distance.
Thus, it may take more FM radio stations to cover a large area. Moreover, the presence of tall buildings or land masses may limit the coverage and quality of FM. Thirdly, FM requires a fairly more complicated receiver and transmitter than an AM signal does. FM radio became popular in the s and early 80s. By the s most music stations switched from AM and adopted FM due to better sound quality. Today, speech broadcasting such as talk and news channels still prefers to use AM, while music channels are solely FM.
AM was initially developed for telephone communication. For radio communication, a continuous wave radio signal called double sideband amplitude modulation DSB-AM was produced. A sideband is a band of frequencies higher called upper sideband or lower called lower sideband than the carrier frequencies which is a result of modulation.
All forms of modulations produce sidebands. The power usage in this system proved inefficient and led to the double-sideband suppressed-carrier DSBSC signal in which the carrier is removed.
For greater efficiency, single-sideband modulation was developed and used in which only a single sideband remained. For digital communication, a simple form of AM called continuous wave CW operation is used in which the presence or absence of carrier wave represents binary data.
The International Telecommunication Union ITU designated different types of amplitude modulation in which include A3E, double sideband full—carrier; R3E, single-sideband reduced-carrier; H3E, single-sideband full-carrier; J3E, single-sideband suppressed-carrier; B8E, independent-sideband emission; C3F, vestigial-sideband and Lincompex, linked compressor and expander.
FM radio characteristics and services include pre-emphasis and de-emphasis, stereophonic FM sound, Quadraphonic sound, Dolby FM and other subcarrier services. Pre-emphasis and de-emphasis are processes that require boosting and reducing certain frequencies. This is done to reduce noise at high frequencies. This uses two or more audio channels independently to produce sound heard from various directions.
Quadraphonic is four-channel FM broadcasting. Dolby FM is a noise reduction system used with FM radio, which has not been very successful, commercially. Below is an old training video from the U.
Army that talks about the technical workings of AM and FM radio. Share this comparison:. If you read this far, you should follow us:.
Diffen LLC, n. I was looking for the difference in sound quality, frequency response. This is very important and should be mentioned. FM radio was developed in the United states in the s, mainly by Edwin Armstrong.
Modulating differences In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted. The frequency and phase remain the same. In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted.
The amplitude and phase remain the same. Pros and cons AM has poorer sound quality compared with FM, but is cheaper and can be transmitted over long distances.
It has a lower bandwidth so it can have more stations available in any frequency range. FM is less prone to interference than AM.
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