IT & Network Solutions
Microwave transmission refers to the technology of transmitting information or energy by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeters; these are called microwaves.
This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.
A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier, and loudspeakers, used to allow a person to address a large public, for example, for announcements of movements at large and noisy air and rail terminals.
The term is also used for systems that may additionally have a mixing console, amplifiers, and loudspeakers suitable for music and speech used to reinforce a sound source, such as recorded music or a person giving a speech or distributing the sound throughout a venue or building. Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars.
PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Intercom systems, installed in many buildings, have microphones in many rooms allowing the occupants to respond to announcements.
Closed-circuit television (CCTV) uses video cameras to transmit a signal to a specific place on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point-to-point (P2P), point-to-multipoint, or mesh wireless links.
Though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that may need monitoring, such as banks, casinos, airports, military installations, and convenience stores. Videotelephony is seldom called "CCTV," but the use of video in distance education, where it is an essential tool, is often so called.
Very high frequency (VHF) is the ITU-designated range of radio frequency electromagnetic waves from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted high frequency (HF), and the following higher frequencies are known as ultra high frequency (UHF).
These names referring to frequency usage originate from the early 20th century, when regular radio services used the terms LF (low frequencies), MF (medium frequencies), and HF (high frequencies). These names were standardized by the International Telecommunications Union (ITU) and extended to higher frequency ranges.
Ultra-high frequency (UHF) designates the ITU radio frequency range of electromagnetic waves between 300 MHz and 3 GHz (3,000 MHz), also known as the decimeter band or decimeter wave, as the wavelengths range from one to ten decimeters, that is 1 decimeter to 1 meter.
Radio waves with frequencies above the UHF band fall into the SHF (super-high frequency) or microwave frequency range. Lower frequency signals fall into the VHF (very high frequency) or lower bands.
UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings, although the transmission through building walls is high enough for indoor reception. They are used for television broadcasting, cordless phones, walkie-talkies, satellite communication, and numerous other applications.
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed carrier (SSB-SC) is a refinement of amplitude modulation that more efficiently uses transmitter power and bandwidth.
Amplitude modulation produces an output signal that has twice the bandwidth of the original baseband signal.
Single-sideband modulation avoids this bandwidth doubling and the power wasted on a carrier at the cost of increased device complexity and more difficult tuning at the receiver.
The Automatic Identification System (AIS) is an automatic tracking system used on ships and by vessel traffic services (VTS) for identifying and locating vessels by electronically exchanging data with other nearby ships,
AIS base stations, and satellites. When satellites are used to detect AIS signatures then the term Satellite-AIS (S-AIS) is used. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport.
Tropospheric scatter (known as "troposcatter" among practitioners) is a method of transmitting and receiving microwave radio signals over considerable distances, often up to 300 km. This propagation method uses the tropospheric scatter phenomenon, where radio waves at particular frequencies are randomly scattered as they pass through the upper layers of the troposphere.
Radio signals are transmitted in a tight beam aimed at the tropopause, midway between the transmitter and receiver sites; as the signals pass through the troposphere, they are scattered, allowing the receiver station to pick up the signal.
A related system is meteor burst communications, which uses the ionized trails of meteors to improve the strength of the scattering.
Television receive-only, TVRO, big ugly dish (BUD), is a term used in North America to refer to the reception of satellite television from FSS-type satellites, generally on C-band analog, free-to-air, and unconnected to a commercial DBS provider. TVRO systems rely on feeds being transmitted unencrypted and using open standards, which heavily contrasts with DBS systems in the region.
The term is rarely used in recent times due to the general move towards pay television and subscription-based DBS services like DirecTV, Dish Network, Bell TV, and Sky TV, although it is still sometimes used to refer to receiving digital TV "backhaul" feeds from FSS-type satellites. TVRO was once the sole, and later the main means of consumer satellite reception in the United States until the mid-1990s and the arrival of services such as PrimeStar, USB, DirecTV, and Dish Network.
While these services are at least theoretically based on open standards (DVB-S, MPEG-2, MPEG-4), the majority of services are encrypted and require proprietary decoder hardware.
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