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VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a quarter wave whip antenna at VHF frequencies is 25 cm to 2.5 meter (10 inches to 8 feet) long. So the VHF and UHF wavelengths are used for two-way radios in vehicles, aircraft, and ...
The disc: The disc should have an overall diameter of 0.7 times a quarter wavelength of the antenna's lowest frequency. The antenna's feed point is at the center of the disc. It is usually fed with 50-ohm coaxial cable, with the center conductor connected to the disc, and the outer conductor to the cone.
Indoor antennas are designed to be located on top of or next to the television set, but are ideally placed near a window in a room and as high up as possible for the best reception. [1] The most common types of indoor antennas are the dipole [2] ("rabbit ears"), which work best for VHF channels, and loop antennas, which work best for UHF. [3]
Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =.
A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; [1] these elements are most often metal rods (or discs) acting as half-wave dipoles. [2]
A quad antenna is a type of directional wire radio antenna used on the HF and VHF bands. A quad is a Yagi–Uda antenna ("Yagi") made from loop elements instead of dipoles: It consists of a driven element and one or more parasitic elements ; however in a quad, each of the loop elements may be square, round, or some other shape.
A typical example, quoted from a commercial hand held VHF or UHF radio, might be: . Receiver sensitivity: 0.25 μV at 12 dB SINAD. This is stating that the receiver will produce intelligible speech with a signal at its input as low as 0.25 μV.