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A very high frequency (VHF) transceiver is a device that is composed of a transmitter and receiver that operates between 30 megahertz (MHz) to 300 megahertz (MHz). The wavelength of a VHF transceiver varies between 39.37 inches (1 m) to 393.70 inches (10 m), mainly depending on the frequency used. Wavelength combined with line-of-sight (LOS) propagation determines VHF devices such as walkie-talkies' and citizen band (CB) radios' receiving and transmitting range.
VHF propagation is generally not affected by the ionosphere in the same manner high frequencies (HF) are. As a result of non-ionospheric interference VHF radio transmissions are restricted to a local area; which prevents cross-talk interference several thousand miles away. Propagation distances for VHF devices also depend on environmental topography, antenna height and several other factors.
In order for VHF transceiver devices to effectively transmit and receive information with one another, LOS radio propagation should not be obstructed. Solid objects such as trees and buildings usually weaken or completely block LOS propagation. HF and ultra-high frequency (UHF) bands are often included in a VHF transceiver device to increase transmission reliability.
Many countries have certain VHF bands restricted to navigational and emergency use. In some countries the VHF radio frequencies of 108 MHz to 118 MHz are reserved for navigational beacons; while 118 MHz to 137 MHz is used for air traffic control. The VHF frequency of 121.5 MHz is often used for emergency signals.
VHF transceiver devices are also used in personal and business use. Personal use of VHF devices usually involves leisure activities where cellular devices are not appropriate. For businesses such as taxi cabs and other transportation industries, base station repeaters are used to extend a VHF device’s communication range.
Transceiver devices vary in aesthetics, radio bands and operating settings. Despite differences in models and settings, basic operating principles remain the same. Most VHF transceivers will have a push-to-talk button for easy and fast communication. The push-to-talk button on most transceivers will allow a party to transmit or communicate to another party on the same frequency and channel. When using the button only one person at a time can transmit while the other is receiving.
For greater peace-of-mind many transceiver devices such as walkie-talkies include encryption and privacy channel options. Without security options sensitive information can still be intercepted by an unauthorized third party. To secure a channel, the walkie-talkie’s encryption function will generate a code or password to be used between parties. Another security option that is often used in conjunction with private codes is the use of voice scrambling.
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