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What is Unguided (Wireless) Media?
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
| Name | Frequency | Wavelength |
|---|---|---|
| Extremely Low Frequency (ELF) | 30 – 300 Hz | 107 to 106m |
| Voice Frequencies (VF) | 300 – 3000 Hz | 106 to 105m |
| Very Low Frequencies (VLF) | 3 – 30 KHz | 105 to 104m |
| Low Frequencies (LF) | 30 – 300 KHz | 104 to 103m |
| Medium Frequencies (MF) | 300 KHz – 3 MHz | 103 to 103m |
| High Frequencies (HF) | 3 – 30 MHz | 102 to 10m |
| Very High Frequencies (VHF) | 30 – 300 MHz | 10 to 1m |
| Ultra-High Frequencies (UHF) | 300 MHz – 3 GHz | 1 to 10-1m |
| Super High Frequencies (SHF) | 3 – 30 GHz | 1-1 to 10-2m |
| Extremely High Frequencies (EHF) | 30 – 300 GHz | 10-2 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
| Name | Frequency | Applications |
|---|---|---|
| 30 Hz – 300 Hz Extremely Low Frequency (ELF) | 104Km to 103Km | Power Transmission |
| 300 Hz – 3 KHz Voice Frequencies (VF) | 103Km to 100Km | Audio Applications |
| 3KHz – 30 KHz Very Low Frequencies (VLF) | 100Km to 10 Km | Submarine 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 1m | TV 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 10-2m | Satellite Communications and Radar |
| 30 – 300 GHz Extremely High Frequencies (EHF) | 10-2 to 10-3m | Satellites and specialized radars |
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