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Showing posts from June, 2019

History of radio § Broadcasting

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Remote control


Radio remote control is the use of electronic control signals sent by radio waves from a transmitter to control the actions of a device at a remote location. Remote control systems may also include telemetry channels in the other direction, used to transmit real-time information of the state of the device back to the control station. Unmanned spacecraft are an example of remote controlled machines, controlled by commands transmitted by satellite ground stations. Most handheld remote controls used to control consumer electronics products like televisions or DVD players actually operate by infrared light rather than radio waves, so are not examples of radio remote control. A security concern with remote control systems is spoofing, in which an unauthorized person transmits an imitation of the control signal to take control of the device. Examples of radio remote control: ·Unamanned aerial vechicle (UAV, drone) – A drone is an aircraft without an onboard pilot, flown by remo…

History of radio § Broadcasting

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Radio location
Radio locating is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar—as well as detecting buried cables, water mains and other public utilities. It is similar to radio navigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radio determination. Radiolocation is also used in real-time locating system (RTLS) for tracking valuable assets.
Basic Principal An object can be located by measuring the characteristics of received radio waves. The radio waves may be transmitted by the object to be located, or they may be backs cattered waves (as in radar or passive RFID). A stud finder uses radiolocation when it uses radio waves rather than ultrasound. One technique measures a distance by using the difference in the power of the received signal strength (RSSI) as compared to…

History of radio § Broadcasting

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                                                     Radar

Radar is a radio location method used to locate and track aircraft, spacecraft, missiles, ships, vehicles, and also to map weather patterns and terrain. A radar set consists of a transmitter and receiver. The transmitter emits a narrow beam of radio waves which is swept around the surrounding space. When the beam strikes a target object, radio waves are reflected back to the receiver. The direction of the beam reveals the object's location. Since radio waves travel at a constant speed close to the speed of light, by measuring the brief time delay between the outgoing pulse and the received "echo", the range to the target can be calculated. The targets are often displayed graphically on a map display called a radar screen. Doppler radar can measure a moving object's velocity, by measuring the change in frequency of the return radio waves due to the Doppler effect. Radar sets mainly use high frequencies in the m…

History of radio § Broadcasting

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                                        Space communication
This is radio communication between a spacecraft and an Earth-based ground station, or another spacecraft. Communication with spacecraft involves the longest transmission distances of any radio links, up to billions of kilometers for interplanetary spacecraft. In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic “dish antennas up to 25 metres (82 ft) in diameter and extremely sensitive receivers. High frequencies in the microwav band are used, since microwaves pass through the ionosphere without refraction, and at microwave frequencies the high gain antennas needed to focus the radio energy into a narrow beam pointed at the receiver are small and take up a minimum of space in a satellite. Portions of the UHF, L,C, S, K, and k band are allocated for space communication. A radio link which transmits data from the Earth's surface to a spacecraft is called an uplink, while…

History of radio § Broadcasting

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                                          Data communications

Wireless Networking: Automated radio links which transmit digital data between computer and other wireless devices using radio waves, linking the devices together transparently in a computer network. Computer networks can transmit any form of data: in addition to email and web pages, they also carry phone call audio, and video content Security is more of an issue for wireless networks than for wired networks since anyone nearby with a wireless modem can access the signal and attempt to log in. The radio signals of wireless networks are encrypted using WPA.

Wireless LAN: based on the IEEE802.11  standards, these are the most widely used computer networks, used to implement local area network  without cables, linking computers, laptops, cell phones, video game consoles, smart TV and printers in a home or office together, and to a wireless router connecting them to the internet with a wire or cable connection. Wireless routers i…

History of radio § Broadcasting

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                             One way voice communication

One way, unidirectional radio transmission is called simplex
Baby Monitor: this is a crib side appliance for mothers of infants that transmits the baby's sounds to a receiver carried by the mother, so she can monitor the baby while she is in other parts of the house. These transmit in FM on 49.300, 49.830, 49.845, 49.860, or 49.875 MHz with low power. Many baby monitors have duplex channels so the mother can talk to the baby, and video cameras to show a picture of the baby, this is called a baby cam. Wireless Microphone: a battery powered microphone with a short range with a short-range transmitter which is handheld or worn on a person's body which transmits its sound by radio to a nearby receiver unit connected to a sound system. Wireless microphones are used by public speakers, performers, and television personalities so they can move freely without trailing a microphone cord. Analog models transmit in FM on Some models t…

History of radio § Broadcasting

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  Two way voice communicationtwo-way radio is an audiotransceiver, a receiver and transmitter in the same device, used for bidirectional person-to-person voice communication. An older term for this mode of communication is radio telephony. The radio link may be half-duplex, as in a walkie-talkie, using a single radio channel in which only one radio can transmit at a time, so different users take turns talking, pressing a "push to talk" button on their radio which switches off the receiver and switches on the transmitter. Or the radio link may be full duplex, a bidirectional link using two radio channels so both people can talk at the same time, as in a cell phone. ·Cell phone – a portable wireless telephone that is connected to the telephone network by radio signals exchanged with a local antenna at a cellular base station (cell tower).The service area covered by the provider is divided into small geographical areas called "cells", each served by a separate base s…

History of radio § Broadcasting

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Bandwidth
A modulated radio wave, carrying an information signal, occupies a range of frequencies. Seediagram. The information (modulation) in a radio signal is usually concentrated in narrow frequency bands called sidebands (SB) just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth (BW). A given amount of bandwidth can carry the same amount of information (data rate in bits per second) regardless of where in the radio frequency spectrum it is located, so bandwidth is a measure of information-carrying capacity. The bandwidth required by a radio transmission depends on the data rate of the information (modulation signal) being sent, and the spectral efficiency of the modulation method used; how much data it can transmit in each kilohertz of bandwidth. Different types of information signals carried by radio have different data rates. For example, a tel…

History of radio § Broadcasting

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Radio communicationIn radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal. The modulation signal may be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter. In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency, called the carrier wave because it serves to "carry" the information through the air. The information signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information on the carrier. Different radio systems use different modulation met…