Wednesday, September 26, 2012

What are the major differences between AM and FM?

Origin: AM method of audio transmission was first successfully carried out in the mid 1870s. FM radio was developed in the United states mainly by Edwin Armstrong in the 1930s.
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. In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted.
Importance: It is used in both analog and digital communication and telemetry. It is used in both analog and digital communication and telemetry.
Pros and cons: AM has poorer sound quality compared to FM, but is cheaper and can be transmitted over long distances. It has a smaller bandwidth so it can have more stations available in any frequency range. FM is less prone to interference than AM. However, FM signals are impacted by physical barriers. FM has greater sound quality due to higher bandwidth.
Stands for: AM stands for Amplitude Modulation FM stands for Frequency Modulation
Range: AM radio ranges from 535 to 1705 kilohertz (OR) Up to 1200 Bits per second FM radio ranges in a higher spectrum from 88 to 108 megahertz. (OR) 1200 to 2400 bits per second
Bandwidth Requirements: Twice the highest modulating frequency. In AM radio broadcasting, the modulating signal has bandwidth of 15kHz, and hence the bandwidth of an amplitude-modulated signal is 30kHz Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth required is 180kHz

What is the difference between Amplitude modulation and frequency modulation?

1. In case of frequency modulation the change in amplitude may be due to noise. If we make use of amplitude limiters in FM receivers then we can completely vanish this noise effect.
2. FM waves are waves having constant amplitude. These are independent of the modulation. So, due to this the power transmission of these waves is also constant. The power transmission of FM waves is better than that of the AM signals.
3. In FM signals, all the transmitted power can be used, but in AM wave the transmission carriers contain most of the power. So, complete use of power is not possible.
4. In FM wave’s noise can be controlled by increasing the deviation up to some amount. This is impossible in case of AM waves.
5. VHF and UHF are the bands of FM broadcasting. In these bands noise effect is very less. But on the other hand bands of AM broadcasting such as MF and HF has higher effects.
6. Co-channel interference can be reduced by using some space wave in FM broadcasting.

The major disadvantages of FM are:

1. Complex apparatus is used to transmit and receive the FM wave.
2. FM waves needs 10 times larger channel width than that of the AM waves.
3. The reception area of FM waves is less than that of AM waves. Due to this wide area communication using the Fm waves is not possible.

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