What is Unguided (Wireless) Media?

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In this type of media, the signal propagates in the form of electromagnetic waves without the requirement of solid media, i.e., in the air. There are also called wireless media.

The electromagnetic spectrum used for wireless communication is shown in the figure −

Propagation Methods

The unguided signals can travel from the transmitter to the receiver in many different ways. The three most important methods are −

  • Ground Wave Propagation
  • SKY Propagation
  • Space propagation or line of sight propagation

Bands

The electromagnetic spectrum is divided into several subbands. The following table shows various frequency bands corresponding to multiple types of propagation and application −

Electromagnetic Waves Band

NameFrequencyWavelength
Extremely Low Frequency (ELF)30 – 300 Hz107 to 106m
Voice Frequencies (VF)300 – 3000 Hz106 to 105m
Very Low Frequencies (VLF)3 – 30 KHz105 to 104m
Low Frequencies (LF)30 – 300 KHz104 to 103m
Medium Frequencies (MF)300 KHz – 3 MHz103 to 103m
High Frequencies (HF)3 – 30 MHz102 to 10m
Very High Frequencies (VHF)30 – 300 MHz10 to 1m
Ultra-High Frequencies (UHF)300 MHz – 3 GHz1 to 10-1m
Super High Frequencies (SHF)3 – 30 GHz1-1 to 10-2m
Extremely High Frequencies (EHF)30 – 300 GHz10-2 to 10-3m
Infrared-0.7 to 10 mm
Visible Light-0.4μm to 0.8μm

EM Spectrum and Communication Application

In the radio communication scheme, the frequencies ranging from a few kilohertz to many gigahertz are being used for several objectives. Let us see the applications of different frequency bands. The frequencies most generally used in early days’ waveform about 300 KHz to 3MHz and were called medium frequencies (MF).

The frequencies in the range of 30 KHz to 300 KHz are known as low frequencies (LF). The frequencies in the range of 3 KHz to 30 KHz are known as very low frequencies (VLF). On the higher frequency side, high frequencies (HF) will wrap the frequency range from 3 MHz to 30 MHz, and the next table gives the components of the entire arable frequency spectrum and its applications.

EM Spectrum with Application

NameFrequencyApplications
30 Hz – 300 Hz
Extremely Low Frequency (ELF)
104Km to 103KmPower Transmission
300 Hz – 3 KHz
Voice Frequencies (VF)
103Km to 100KmAudio Applications
3KHz – 30 KHz
Very Low Frequencies (VLF)
100Km to 10 KmSubmarine communications, Navy, Military Communications
30KHz – 300 KHz
Low Frequencies (LF)
10 Km to 1Km
Long waves
Aeronautical and marine navigation frequencies act as subcarriers.
300 KHz – 30 MHz
Medium Frequencies (MF)
1 Km to 100 m
Medium Waves
AM radio broadcast, Marine and aeronautical communications
3 MHz – 30 MHz
High Frequencies (HF)
100 m to 10 m
Short Waves
Short-waves transmission, Amateur and CB communication
30 MHz – 300 MHz
Very High Frequencies (VHF)
10 m to 1mTV broadcasting, FM broadcasting
300 MHz – 3 GHz
Ultra-High Frequencies (UHF)
1m to 10 cm
Microwaves
UHF TV channels, cellular phone Military applications
3 GHz – 30 GHz
Super High Frequencies (SHF)
10-1m to 10-2mSatellite Communications and Radar
30 – 300 GHz
Extremely High Frequencies (EHF)
10-2 to 10-3mSatellites and specialized radars
raja
Published on 04-May-2021 15:19:35
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