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Saturday, 29 May 2021

Radio Frequency Bandwidth of the Signal


Radio Frequency Bandwidth of the Signal

The frequency range (i.e., bandwidth) required for a given transmission is depend on the bandwidth occupied by the modulation signals itself. For example, a high -fidelity audio- signal which occupies the range 50 Hz to 15 KHz requires a bandwidth of 300 to 3400 Hz for a telephone conservation. If the same carrier has been similarly modulated a more bandwidth signal the modulated wave bandwidth will also increases. However the transmitted signal bandwidth need not be exactly same as the bandwidth of original signal. Also it is necessary to know the bandwidth of modulating signal itself before finding the bandwidth of modulated signal. If the orrginal signals are sinusoidal in nature, the bandwidth is simply the frequency range between the lowest and the highest sine-wave signal. This creates no difficulty. However, if the modulating signals are non-sinusoidal in nature, then much more complexity arises.


In the selection of a particular carrier frequency for a given application, there are number of considerations, but most important is the width of the frequency band covered by the signal components. In television broadcasting, where each radio frequencies channel width is 6 MHz, high carrier frequencies must be employed for interference free reception. A similar requirement applies to frequency modulated sound broadcasts. Radio frequency bandwidths covered by different types of signal and the carrier frequencies at which signals are normally transmitted are shown in table


Sl No:

Type of Signal

Radio Frequency Transmission Bandwidth

Typical Carrier Frequency Ranges


Telegraphy signals

80 Hz – 2 KHz

18 KHz – 30 MHz


Telephony signals and AM signals

10 KHz

500 KHz – 30 MHz


FM signals

150 KHz

88 MHz – 108 MHz


Facsimile signals

6 KHz

500 KHz – 30 MHz


Television signals

6 MHz

54 MHz – 216 MHz


Radar signals

2 MHz – 10 MHz

200 MHz – 30,000 MHz


Radio waves Classification


The frequencies, used for radio communication will range from 15 KHz to more than 30000 MHz. The selection of a particular carrier frequency for a particular application depends upon number of factors: From the Electromagnetic -Spectrum which extends through audio frequencies (20 Hz to 15 KHz), radio frequencies (15 KHz to 300,000 MHz), the infra-red region, the visible light region, the ultraviolet region and X-rays, γ-rays, cosmic rays etc., our interest at present for radio communication purposes is specially with radio frequencies and with audio frequencies to some extent. The radio and audio frequency range is subdivided as shown in table below. The wavelength can be find by the using the equation f = c/λ, where c is velocity of light, f is frequency and λ wavelength.


Sl No:


Frequency range


Audio frequency, AF

20 – 2500 Hz


High Audio Frequency, HAF

2500 – 5000 Hz


Very Low Frequency, VLF

10 – 30 KHz


Low Frequency, LF

30 – 300 KHz


Medium Frequency, MF

300 – 3,000 KHz


High Frequency, HF

3,000 – 30,000 KHz (3 – 30 MHz)


Very High Frequency, VHF

30 – 300 MHz


Ultra High Frequency, UHF

300 – 3,000 MHz


Super High Frequency, SHF

3,000 – 30,000 MHz (3 – 30 GHz)


Extremely High Frequency, EHF

30 – 300 GHz


Note: Frequencies more than about 2000 MHz are generally referred to as micro wave frequencies.

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