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Demand Assigned Multiple Access (DAMA) is a technology used to assign a channel to clients that do not need to use it constantly. DAMA systems assign communication channels based on news issued from user terminals to a network security system.
MURS range will vary, depending on antenna size and placement. With an external antenna, ranges of 10 miles (16 km) or more can be expected. [8] Since MURS radios use frequencies in the VHF business band, they are subject to obstructions in line of sight, which includes the curvature of the Earth.
A desirable null exists if the transmit antenna is located exactly below the receive antenna beyond a minimum distance. Almost the same isolation as a low-grade duplexer (about −60 decibels) can be accomplished by installing the transmit antenna below, and along the centerline of, the receive antenna.
In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer. Duplexers can be based on frequency (often a waveguide filter), polarization (such as an orthomode transducer), or timing (as is typical in radar). [1]
Antenna diversity, also known as space diversity or spatial diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight (LOS) between transmitter and receiver. Instead the ...
The television broadcast bands are too wide in frequency to be covered by a single antenna, so the two options are separate antennas used for the VHF and UHF bands or a combination (combo) VHF/UHF antenna. [6] A VHF/UHF antenna combines two antennas feeding the same feedline mounted on the same support boom.
In essence, a trunked radio system is a packet switching computer network. Users' radios send data packets to a computer, operating on a dedicated frequency — called a control channel — to request communication on a specific talkgroup.
A Goubau line or Sommerfeld–Goubau line, [1] or G-line for short, is a single-wire transmission line used to conduct radio waves at UHF and microwave frequencies. [2] [3] [4] The dielectric coated transmission line was invented by F. Harms [5] in 1907 and George J. E. Goubau [6] in 1950, based on work on surface waves on wires from 1899 by Arnold Sommerfeld.