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So the VHF and UHF wavelengths are used for two-way radios in vehicles, aircraft, and handheld transceivers and walkie-talkies. Portable radios usually use whips or rubber ducky antennas, while base stations usually use larger fiberglass whips or collinear arrays of vertical dipoles.
Many businesses and industries throughout the world use these radios as their primary means of communication, especially from a fixed location to mobile users (i.e. from a base site to a fleet of mobiles). Commercial radios are typically available in the VHF and UHF frequency bands. 30−50 MHz (sometimes called "Low VHF Band" or "Low Band ...
Although no real antenna can be exactly isotropic, a few antennas are built to be as near to isotropic as possible; they are used for emergency backup antennas and for test equipment for other antennas: Because the received and transmitted signal strength is the same in (almost) every direction, they work without any need for them to be any ...
In some large metropolitan areas, such as New York, the UHF-T band (between 470 and 512 MHz) is also used due to congestion on the standard VHF or UHF bands. There are also a number of specific frequencies, in both the VHF and UHF spectrums, that are for business use; some of these have color-coded names, such as Red Dot or Blue Star.
After the 1973 oil crisis, the U.S. government imposed a nationwide 55 mph speed limit, and fuel shortages and rationing were widespread.Drivers (especially commercial truckers) used CB radios to locate service stations with better supplies of fuel, to notify other drivers of speed traps, and to organize blockades and convoys in a 1974 strike protesting the new speed limit and other trucking ...
German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the vertical or monopole antenna.