Why AM is used for long distance communication?

Electronics Engineering Questions

Answers.com > Wiki Answers > Categories > Technology > Engineering > Electronics Engineering Best AnswerAM has a frequency range of 531 kHz to 1602 kHz and on the other hand FM has a frequency range between 8705 MHz to 108 MHz. If we talk about the bandwidth of AM then it is 1071 KHz and bandwidth of FM is 20.5 MHz. According to the bandwidth FM should be used for long distance transmission but it is not used for long distance but AM is used fir long distance transmissions. the answer is here. Long distance transmissions are also decided by the Spectrum of the Signal in frequency domain by doing the Fourier transform of the Signal.If we draw the Spectrum of AM waves the we find that their is a main loop in the central part of the spectrum with a high frequency and on the left and right side of this loop their are side loop which are very smaller then the main loop. In FM information can be recover from the main loop only not from the side loops. On the other hand in AM waves all the loops in spectrum is of same size and information can be recover from all the loops. That is why AM is used for long distance transmission.Thnx -Vipin Jasoria

Why F.M is not used for long distance communication compared to A.M?

5 years ago Report Abuse

tlbs101

Best Answer - Chosen by Voters

It is not the fact that one is FM and one is AM, it is the fact that AM is broadcast on a much lower frequency (around 1 MHz) compared with FM which is broadcast around 100 MHz. If you had a transmitter at 1 MHz and decided to use FM instead of AM, it would still be heard at long distances

under the same conditions that AM is heard.

The very simplistic explanation is: lower frequency waves travel further because they can interact with (bounce off) the ionosphere under certain conditions, whereas frequencies above a few 10s of MHz cannot 'bounce' off the ionosphere. Waves that bounce off the ionosphere can travel over the horizon for very long distances.

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5 years ago Report Abuse

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Other Answers (3)

HR

in AM carrier amplitude varies with modulation signal / amplitude

so over a long distance the signal degradation may take place as well as noise may override the signal

so for FM we don't face this problem as amplitude is fixed throughout and frequency is varying

w hy am is

which can be obtained at long distance by knowing carrier and modulation freqalsowe can use filters to eliminate other freqs

Thank you

o 5 years agoo Report Abuse

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Pradeep S

The FM carrier frequencies have very short wave lengths and travel almost in straight lines, therefore when the signals are beamed from a source they move away from the surface due to the earth's curvature as the distance from the originating source increases. The AM signals have longer wave lengths and hence have a tendency to bend over the surface thereby covering larger distances.

o 5 years agoo Report Abuse

8% 4 Votes

Mano

One of the drawbacks of wideband FM is the large bandwidth required. Commercial FM broadcasting requires 150 KHz of bandwidth to transmit a15 KHz audio signal, 5 times the bandwidth required for an AM signal.

The output powers used can range from 10 mW to 100 kW. Note that FM is not used at frequencies below approximately 30 MHz.

FM is used in the following applications:Non-commercial broadcasting from 88 – 90 MHz (WFM) Commercial broadcasting from 90 – 108 MHz (WFM) Television audio (WFM) Public Service communications (police, fire departments, etc.) from 30 – 50 MHz, 136-174 MHz, 450-470 MHz, and 800 MHz (NBFM)

Amateur Radio Service Communications 29.5 – 29.7 MHZ, 52 – 54 MHz, 144 – 148 MHz, 222 – 225 MHz, 440 – 450 MHz, 902 MHz, 1240 – 1300 MHz, and other frequencies above 2.3 GHz (NBFM)

Point-to-point microwave links used by telecommunications companies (this is very wideband FM – the deviation of the carrier can be 10 MHz or more).