Digital terrestrial television
Digital terrestrial television is a technology for broadcast television in which land-based television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, has replaced analog, in common use since the middle of the 20th century. Test broadcasts began in 1998 with the changeover to DTTV beginning in 2006 and is now complete in many countries; the advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, lower operating costs for broadcasters. Different countries have adopted different digital broadcasting standards; the amount of data that can be transmitted is directly affected by channel capacity and the modulation method of the transmission. North America uses the ATSC standard with 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analog television.
This provides more immunity to interference, but is not immune to multipath distortion and does not provide for single-frequency network operation. The modulation method in DVB-T is COFDM with either 16-state Quadrature Amplitude Modulation. In general, 64QAM is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important program streams. This is called hierarchical modulation. DVB-T are designed to work in single frequency networks. Developments in video compression have resulted in improvements on the original H.262 MPEG 2 codec, surpassed by H.264/MPEG-4 AVC and more H.265 HEVC. H.264 enables three high-definition television services to be coded into a 24 Mbit/s DVB-T European terrestrial transmission channel. DVB-T2 increases this channel capacity to 40 Mbit/s, allowing more services. DTTV is received either via a digital set-top box, TV gateway or more now an integrated tuner included with television sets, that decodes the signal received via a standard television antenna.
These devices now include digital video recorder functionality. However, due to frequency planning issues, an aerial capable of receiving a different channel group may be required if the DTTV multiplexes lie outside the reception capabilities of the installed aerial; this is quite common in the UK. Indoor aerials are more to be affected by these issues and need replacing. Main articles: List of digital television deployments by country, Digital television transition Afghanistan launched digital transmissions in Kabul using DVB-T2/MPEG-4 on Sunday, 31 August 2014. Test transmissions had commenced on 4 UHF channels at the start of June 2014. Transmitters were provided by GatesAir. Bangladesh had its first DTT service DVB-T2 / MPEG-4 on April 2016 launched by the GS Group; the service is called RealVU. It is done with partnership with Beximco. GS Group acts as a supplier and integrator of its in-house hardware and software solutions for the operator's functioning in accordance with the modern standards of digital television.
RealVu provides more than 100 TV channels in HD quality. The digital TV set-top boxes developed by GS Group offer such functions as PVR and time-shift, along with an EPG. India adopted DVB-T system for digital television in July 1999; the first DVB-T transmission was started on 26 January 2003 in the four major metropolitan cities by Doordarshan. The terrestrial transmission is available in both digital and analog formats. 4 high power DVB-T transmitters were set up in the top 4 cities, which were upgraded to DVB-T2 + MPEG4 and DVB-H standards. An additional 190 high power, 400 low power DVB-T2 transmitters have been approved for Tier I, II and III cities of the country by 2017; the Indian telecom regulator, TRAI, had recommended the I&B to allow private broadcast companies to use the DTT technology, in 2005. So far, the Indian I&B ministry only permits private broadcast companies to use satellite, cable and IPTV based systems; the government's broadcasting organisation Doordarshan had started the free TV service over DVB - T2 to the mobile phone users from February 25 onwards and extended to cover 16 cities including the four metros from April 5, 2016.
Israel started digital transmissions in MPEG-4 on Sunday, August 2, 2009, anal
Digital Video Broadcasting - Satellite - Second Generation is a digital television broadcast standard, designed as a successor for the popular DVB-S system. It was developed in 2003 by the DVB Project, an international industry consortium, ratified by ETSI in March 2005; the standard is based on, improves upon DVB-S and the electronic news-gathering system, used by mobile units for sending sounds and images from remote locations worldwide back to their home television stations. DVB-S2 is envisaged for broadcast services including standard and HDTV, interactive services including Internet access, data content distribution; the development of DVB-S2 coincided with the introduction of HDTV and H.264 video codecs. Two new key features that were added compared to the DVB-S standard are: A powerful coding scheme based on a modern LDPC code. For low encoding complexity, the LDPC codes chosen have a special structure known as Irregular Repeat-Accumulate codes. VCM and ACM modes, which allow optimizing bandwidth utilization by dynamically changing transmission parameters.
Other features include enhanced modulation schemes up to 32APSK, additional code rates, the introduction of a generic transport mechanism for IP packet data including MPEG-4 audio–video streams, while supporting backward compatibility with existing MPEG-2 TS based transmission. DVB-S2 achieves better performance than its predecessors – allowing for an increase of available bitrate over the same satellite transponder bandwidth; the measured DVB-S2 performance gain over DVB-S is around 30% at the same satellite transponder bandwidth and emitted signal power. When the contribution of improvements in video compression is added, an HDTV service can now be delivered in the same bandwidth that supported an early DVB-S based MPEG-2 SDTV service only a decade before. In March 2014, DVB-S2X specification has been published by DVB Project as an optional extension adding further improvements. Direct input of one or more MPEG-2 Transport Streams. MPEG-TS is supported using a compatibility mode; the native stream format for DVB-S2 is called Generic Stream, can be used to efficiently carry IP-based data, including MPEG-4 AVC/H.264 services.
Backward compatibility to DVB-S, intended for end users, DVB-DSNG, used for backhauls and electronic news gathering. Variable coding and modulation to optimize bandwidth utilization based on the priority of the input data. Adaptive coding and modulation to allow flexibly adapting transmission parameters to the reception conditions of terminals, e.g. switching to a lower code rate during fading. Four modulation modes: QPSK and 8PSK are proposed for broadcast applications, can be used in non-linear transponders driven near to saturation. 16APSK and 32APSK are used for professional, semi-linear applications, but can be used for broadcasting though they require a higher level of available C/N and an adoption of advanced pre-distortion methods in the uplink station in order to minimize the effect of transponder nonlinearity. Improved rolloff: α = 0.20 and α = 0.25 in addition to the roll-off of DVB-S α = 0.35. Improved coding: a modern large LDPC code is concatenated with an outer BCH code to achieve quasi-error-free reception conditions on an AWGN channel.
The outer code is introduced to avoid error floors at low bit-error rates. A single forward error correction or FEC frame may have 16,200 bits. If VCM or ACM is used, the broadcast can be a combination of short frames. Several code rates for flexible configuration of transmission parameters: 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 6/7, 8/9, 9/10. Code rates 1/4, 1/3, 2/5 have been introduced for exceptionally poor reception conditions in combination with QPSK modulation. Encoding values 9/10 behave poorly under marginal link conditions. However, with targeted spot Ku or Ka band downlinks these code rates may be recommended to prevent out-of-region viewing for copyright or cultural reasons. Optional input stream synchronization to provide a constant end-to-end delay. Depending on code rate and modulation, the system can operate at a C/N between −2.4 dB and 16 dB with a quasi-error free goal of a 10−7 TS packet error rate. Distance to the Shannon limit ranges from 0.7 dB to 1.2 dB. Modes and features of DVB-S2 in comparison to DVB-S: Envisaged scenarios for DVB-S2 by the standard document are: Broadcasting television services in SDTV or HDTV.
Optionally, this transmission may be backwards compatible with DVB-S, but does not benefit from the 30% extra bandwidth. Interactive services including Internet access. Data generated by the user may be sent by mobile wireless, or satellite uplink. Professional applications, where data must be multiplexed in real time and broadcast in the VHF/UHF band; these transmissions are not intended for the average viewer. Large-scale data content distribution; these include point-to-point and multicast services, as well as transmission to head-ends for distribution over other media. The conversion process from DVB-S to DVB-S2 is being accelerated, due to the rapid increase of HDTV and introduction of 3D-HDTV; the main factor slowing down this process is the need to replace or upgrade set-top boxes, or acquire TVs with DVB-S2 integrated tuners, which makes the transition slower for established operators. Cu
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter. Different sources define different frequency ranges as microwaves. A more common definition in radio engineering is the range between 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations; the prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. Rather, it indicates that microwaves are "small", compared to the radio waves used prior to microwave technology; the boundaries between far infrared, terahertz radiation and ultra-high-frequency radio waves are arbitrary and are used variously between different fields of study. Microwaves travel by line-of-sight. At the high end of the band they are absorbed by gases in the atmosphere, limiting practical communication distances to around a kilometer.
Microwaves are used in modern technology, for example in point-to-point communication links, wireless networks, microwave radio relay networks, radar and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, for cooking food in microwave ovens. Microwaves occupy a place in the electromagnetic spectrum with frequency above ordinary radio waves, below infrared light: In descriptions of the electromagnetic spectrum, some sources classify microwaves as radio waves, a subset of the radio wave band; this is an arbitrary distinction. Microwaves travel by line-of-sight paths. Although at the low end of the band they can pass through building walls enough for useful reception rights of way cleared to the first Fresnel zone are required. Therefore, on the surface of the Earth, microwave communication links are limited by the visual horizon to about 30–40 miles.
Microwaves are absorbed by moisture in the atmosphere, the attenuation increases with frequency, becoming a significant factor at the high end of the band. Beginning at about 40 GHz, atmospheric gases begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies. Above 100 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. In a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal; this technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon, at distances up to 300 km.
The short wavelengths of microwaves allow omnidirectional antennas for portable devices to be made small, from 1 to 20 centimeters long, so microwave frequencies are used for wireless devices such as cell phones, cordless phones, wireless LANs access for laptops, Bluetooth earphones. Antennas used include short whip antennas, rubber ducky antennas, sleeve dipoles, patch antennas, the printed circuit inverted F antenna used in cell phones, their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore, beams of microwaves are used for point-to-point communication links, for radar. An advantage of narrow beams is that they don't interfere with nearby equipment using the same frequency, allowing frequency reuse by nearby transmitters. Parabolic antennas are the most used directive antennas at microwave frequencies, but horn antennas, slot antennas and dielectric lens antennas are used. Flat microstrip antennas are being used in consumer devices.
Another directive antenna practical at microwave frequencies is the phased array, a computer-controlled array of antennas which produces a beam which can be electronically steered in different directions. At microwave frequencies, the transmission lines which are used to carry lower frequency radio waves to and from antennas, such as coaxial cable and parallel wire lines, have excessive power losses, so when low attenuation is required microwaves are carried by metal pipes called waveguides. Due to the high cost and maintenance requirements of waveguide runs, in many microwave antennas the output stage of the transmitter or the RF front end of the receiver is located at the antenna; the term microwave has a more technical meaning in electromagnetics and circuit theory. Apparatus and techniques may
Wi-Fi is technology for radio wireless local area networking of devices based on the IEEE 802.11 standards. Wi‑Fi is a trademark of the Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that complete after many years of testing the 802.11 committee interoperability certification testing. Devices that can use Wi-Fi technologies include, among others and laptops, video game consoles and tablets, smart TVs, digital audio players, digital cameras and drones. Wi-Fi compatible devices can connect to the Internet via a wireless access point; such an access point has a range of about 20 meters indoors and a greater range outdoors. Hotspot coverage can be as small as a single room with walls that block radio waves, or as large as many square kilometres achieved by using multiple overlapping access points. Different versions of Wi-Fi exist, with radio bands and speeds. Wi-Fi most uses the 2.4 gigahertz UHF and 5 gigahertz SHF ISM radio bands. Each channel can be time-shared by multiple networks.
These wavelengths work best for line-of-sight. Many common materials absorb or reflect them, which further restricts range, but can tend to help minimise interference between different networks in crowded environments. At close range, some versions of Wi-Fi, running on suitable hardware, can achieve speeds of over 1 Gbit/s. Anyone within range with a wireless network interface controller can attempt to access a network. Wi-Fi Protected Access is a family of technologies created to protect information moving across Wi-Fi networks and includes solutions for personal and enterprise networks. Security features of WPA have included stronger protections and new security practices as the security landscape has changed over time. In 1971, ALOHAnet connected the Hawaiian Islands with a UHF wireless packet network. ALOHAnet and the ALOHA protocol were early forerunners to Ethernet, the IEEE 802.11 protocols, respectively. A 1985 ruling by the U. S. Federal Communications Commission released the ISM band for unlicensed use.
These frequency bands are the same ones used by equipment such as microwave ovens and are subject to interference. In 1991, NCR Corporation with AT&T Corporation invented the precursor to 802.11, intended for use in cashier systems, under the name WaveLAN. The Australian radio-astronomer Dr John O'Sullivan with his colleagues Terence Percival, Graham Daniels, Diet Ostry, John Deane developed a key patent used in Wi-Fi as a by-product of a Commonwealth Scientific and Industrial Research Organisation research project, "a failed experiment to detect exploding mini black holes the size of an atomic particle". Dr O'Sullivan and his colleagues are credited with inventing Wi-Fi. In 1992 and 1996, CSIRO obtained patents for a method used in Wi-Fi to "unsmear" the signal; the first version of the 802.11 protocol was released in 1997, provided up to 2 Mbit/s link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds, this proved to be popular. In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most products are sold.
Wi-Fi uses a large number of patents held by many different organizations. In April 2009, 14 technology companies agreed to pay CSIRO $1 billion for infringements on CSIRO patents; this led to Australia labeling Wi-Fi as an Australian invention, though this has been the subject of some controversy. CSIRO won a further $220 million settlement for Wi-Fi patent-infringements in 2012 with global firms in the United States required to pay the CSIRO licensing rights estimated to be worth an additional $1 billion in royalties. In 2016, the wireless local area network Test Bed was chosen as Australia's contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia; the name Wi-Fi, commercially used at least as early as August 1999, was coined by the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a name, "a little catchier than'IEEE 802.11b Direct Sequence'." Phil Belanger, a founding member of the Wi-Fi Alliance who presided over the selection of the name "Wi-Fi", has stated that Interbrand invented Wi-Fi as a pun on the word hi-fi, a term for high-quality audio technology.
Interbrand created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification of a product for interoperability; the Wi-Fi Alliance used the advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created. While inspired by the term hi-fi, the name was never "Wireless Fidelity"; the Wi-Fi Alliance was called the "Wireless Fidelity Alliance Inc" in some publications. Non-Wi-Fi technologies intended for fixed points, such as Motorola Canopy, are described as fixed wireless. Alternative wireless technologies include mobile phone standards, such as 2G, 3G, 4G, LTE; the name is sometimes written as WiFi, Wifi, or wifi, but these are not approved by the Wi-Fi Alliance. IEEE is a separate, but related organization and their website has stated "WiFi is a short name for Wireless Fidelity". To connect to a Wi-Fi LAN, a computer has to be equipped with a wireless network interface controller; the combination of computer and interface controllers is called a station.
A service set is the set of all the devices associated with a particular Wi-Fi network. The service set can be local, extended or mesh; each service set has an associated identifier, the 32-byte Service Set Identifier, which identifies the partic
IEEE 802.20 or Mobile Broadband Wireless Access was a specification by the standard association of the Institute of Electrical and Electronics Engineers for mobile wireless Internet access networks. The main standard was published in 2008. MBWA is no longer being developed; this wireless broadband technology is known and promoted as iBurst. It was developed by ArrayComm and optimizes the use of its bandwidth with the help of smart antennas. Kyocera is the manufacturer of iBurst devices. IBurst is a mobile broadband wireless access system, first developed by ArrayComm, announced with partner Sony in April 2000, it was adopted as the High Capacity – Spatial Division Multiple Access radio interface standard by the Alliance for Telecommunications Industry Solutions. The standard was prepared by ATIS’ Wireless Technology and Systems Committee’s Wireless Wideband Internet Access subcommittee and accepted as an American National Standard in 2005. HC-SDMA was announced as considered by ISO TC204 WG16 for the continuous communications standards architecture, known as Communications, Air-interface and Medium range, which ISO is developing for intelligent transport systems.
ITS may include applications for public safety, network congestion management during traffic incidents, automatic toll booths, more. An official liaison was established between WTSC and ISO TC204 WG16 for this in 2005; the HC-SDMA interface provides wide-area broadband wireless data-connectivity for fixed and mobile computing devices and appliances. The protocol is designed to be implemented with smart antenna array techniques to improve the radio frequency coverage and performance for the system. In January 2006, the IEEE 802.20 Mobile Broadband Wireless Access Working Group adopted a technology proposal that included the use of the HC-SDMA standard for the 625kHz Multi-Carrier time division duplex mode of the standard. One Canadian vendor operates at 1.8 GHz. The HC-SDMA interface operates on a similar premise as cellular phones, with hand-offs between HC-SDMA cells providing the user with a seamless wireless Internet access when moving at the speed of a car or train; the standard's proposed benefits: IP roaming & handoff New MAC and PHY with IP and adaptive antennas Optimized for full mobility up to vehicular speeds of 250 km/h Operates in Licensed Bands Uses Packet Architecture Low LatencySome technical details were: Bandwidths of 5, 10, 20 MHz.
Peak data rates of 80 Mbit/s. Spectral efficiency above 1 bit/sec/Hz using multiple input/multiple output technology. Layered frequency hopping allocates OFDM carriers to near and far-away handsets, improving SNR Supports low-bit rates efficiently, carrying up to 100 phone calls per MHz. Hybrid ARQ with up to 6 transmissions and several choices for interleaving. Basic slot period of 913 microseconds carrying 8 OFDM symbols. One of the first standards to support both TDM and separate-frequency deployments; the protocol: specifies base station and client device RF characteristics, including output power levels, transmit frequencies and timing error, pulse shaping, in-band and out-of band spurious emissions, receiver sensitivity and selectivity. The protocol supports Layer 3 mechanisms for creating and controlling logical connections between client device and base including registration, stream start, power control, link adaptation, stream closure, as well as L3 mechanisms for client device authentication and secure transmission on the data links.
Deployed iBurst systems allow connectivity up to 2 Mbit/s for each subscriber equipment. There will be future firmware upgrade possibilities to increase these speeds up to 5 Mbit/s, consistent with HC-SDMA protocol; the 802.20 working group was proposed in response to products using technology developed by ArrayComm marketed under the iBurst brand name. The Alliance for Telecommunications Industry Solutions adopted iBurst as ATIS-0700004-2005; the Mobile Broadband Wireless Access Working Group was approved by IEEE Standards Board on December 11, 2002 to prepare a formal specification for a packet-based air interface designed for Internet Protocol-based services. At its height, the group had 175 participants. On June 8, 2006, the IEEE-SA Standards Board directed that all activities of the 802.20 Working Group be temporarily suspended until October 1, 2006. The decision came from complaints of a lack of transparency, that the group's chair, Jerry Upton, was favoring Qualcomm; the unprecedented step came after other working groups had been subject to related allegations of large companies undermining the standard process.
Intel and Motorola had filed appeals. These claims were cited in a 2007 lawsuit filed by Broadcom against Qualcomm. On September 15, 2006, the IEEE-SA Standards Board approved a plan to enable the working group to move towards completion and approval by reorganizing; the chair at the November 2006 meeting was Arnold Greenspan. On July 17
Multichannel Multipoint Distribution Service
Multichannel Multipoint Distribution Service known as Broadband Radio Service and known as Wireless Cable, is a wireless telecommunications technology, used for general-purpose broadband networking or, more as an alternative method of cable television programming reception. MMDS is used in the Sudan, United States, Mexico, Dominican Republic, Ukraine, Slovakia, Brazil, Australia, Madeira, Czech Republic, Nigeria, Panama, Sri Lanka, Uruguay, Belarus, Cambodia and Kyrgyzstan, it is most used in sparsely populated rural areas, where laying cables is not economically viable, although some companies have offered MMDS services in urban areas, most notably in Ireland, until they were phased out in 2016. The BRS band uses microwave frequencies from 2.5 GHz to 2.7 GHz. Reception of BRS-delivered television and data signals is done with a rooftop microwave antenna; the antenna is attached to a down-converter or transceiver to receive and transmit the microwave signal and convert them to frequencies compatible with standard TV tuners, some antennas use an integrated down-converter or transceiver.
Digital TV channels can be decoded with a standard cable set-top box or directly for TVs with integrated digital tuners. Internet data can be received with a standard DOCSIS Cable Modem connected to the same antenna and transceiver; the MMDS band is separated into 33 6 MHz "channels" which may be licensed to cable companies offering service in different areas of a country. The concept was to allow entities to own several channels and multiplex several television and Internet data onto each channel using digital technology. Just like with Digital Cable channels, each channel is capable of 30.34 Mbit/s with 64QAM modulation, 42.88 Mbit/s with 256QAM modulation. Due to forward error correction and other overhead, actual throughput is around 27 Mbit/s for 64QAM and 38 Mbit/s for 256QAM; the newer BRS Band Plan makes changes to channel size and licensing in order to accommodate new WIMAX TDD fixed and mobile equipment, reallocated frequencies from 2150–2162 MHz to the AWS band. These changes may not be compatible with the frequencies and channel sizes required for operating traditional MMDS or DOCSIS based equipment.
Local Multipoint Distribution Service and BRS have adapted the DOCSIS from the cable modem world. The version of DOCSIS modified for wireless broadband is known as DOCSIS+. Data-transport security is accomplished under BRS by encrypting traffic flows between the broadband wireless modem and the WMTS located in the base station of the provider's network using Triple DES. DOCSIS+ reduces theft-of-service vulnerabilities under BRS by requiring that the WMTS enforce encryption, by employing an authenticated client/server key-management protocol in which the WMTS controls distribution of keying material to broadband wireless modems. LMDS and BRS wireless modems utilize the DOCSIS+ key-management protocol to obtain authorization and traffic encryption material from a WMTS, to support periodic reauthorization and key refresh; the key-management protocol uses X.509 digital certificates, RSA public key encryption, Triple DES encryption to secure key exchanges between the wireless modem and the WMTS.
MMDS provided greater range than LMDS. MMDS may be obsoleted by the newer 802.16 WiMAX standard approved since 2004. MMDS was sometimes expanded to Multipoint Microwave Distribution System or Multi-channel Multi-point Distribution System. All three phrases refer to the same technology. In the United States, WATCH Communications, Eagle Vision, several other companies offer MMDS-based wireless cable television, Internet access, IP-based telephone services. In certain areas, BRS is being deployed for use as wireless high-speed Internet access in rural areas where other types of high-speed internet are either unavailable or prohibitively expensive. CommSPEED is a major vendor in the US market for BRS-based internet. AWI Networks operates a number of MMDS sites delivering high-speed Internet, VoIP telephone, Digital TV services in the Southwestern U. S. In 2010, AWI began upgrading its infrastructure to DOCSIS 3.0 hardware, along with new microwave transmission equipment, allowing higher modulation rates like 256QAM.
This has enabled download speeds in excess of 100 Mbit/s, over distances up to 35 miles from the transmission site. In the early days of MMDS, it was known as "Wireless Cable" and was used in a variety of investment scams that still surface today. Frequent solicitations of Wireless Cable fraud schemes were heard on talk radio shows like The Sonny Bloch Show in the mid-1990s. Several US telephone companies attempted television services via this system in the mid-1990s – the Tele-TV venture of Bell Atlantic, NYNEX and Pacific Bell; the Tele-TV operation was only launched from 1999 to 2001 by Pacific Bell, while Americast petered out by that time, albeit in GTE and BellSouth areas. In the Canadian provinces of Manitoba and British Columbia, Craig Wireless operates a wireless cable and internet service for rural and remote customers. In Mexico, the 2.5 GHz band spectrum was reclaimed by th
Amateur television is the transmission of broadcast quality video and audio over the wide range of frequencies of radio waves allocated for radio amateur use. ATV is used for non-commercial experimentation and public service events. Ham TV stations were on the air in many cities before commercial television stations came on the air. Various transmission standards are used, these include the broadcast transmission standards of NTSC in North America and Japan, PAL or SECAM elsewhere, utilizing the full refresh rates of those standards. ATV includes the study of building of such transmitters and receivers, the study of radio propagation of signals travelling between transmitting and receiving stations. ATV is an extension of amateur radio, it is called HAM TV or fast-scan TV, as opposed to slow-scan television. SSTV is a method of transmitting still images over radio. In North America, amateur radio bands that are suitable for a television signal are higher in frequency than VHF broadcast TV; the lowest frequency ham band suitable for television transmission is 70 centimeters, between broadcast channels 13 and 14.
While outside of broadcast television channels, this frequency falls into CATV frequencies, on channels 57 to 61. As such, ATV transmissions can be viewed by setting a television or analog cable-box to cable input and attaching an outdoor antenna. For more sensitive reception, some users may use a purposely-built ATV down-converter, a kind of set-top-box. Other bands are used for ATV, most of them in the UHF region on frequencies higher than UHF broadcast TV. 33 centimeters and 23 centimeters are two other used bands for ATV, but reception of these higher bands requires the use of a down-converter. Most ATV signals are transmitted in either amplitude modulation or vestigial sideband NTSC. DSB AM and VSB AM signals are inherently compatible with each other, most televisions can receive either. DSB-AM signals consists of both upper and lower sidebands. VSB-AM is where DSB-AM is filtered and the lower sideband is attenuated at frequencies more than 1.25 MHz from the carrier signal. A VSB filter can be added to a DSB-AM transmitter to make it a VSB signal.
The filters, depending on power usage, will cost anywhere from US$100–1,000. For practical reasons, most individual ATV users transmit in DSB-AM, VSB is transmitted by repeater stations. On the 33 cm and higher bands, frequency modulation ATV may be used, on the SHF and EHF ham bands, FM is more used than VSB or AM. FM ATV is incompatible with AM/VSB ATV, a separate demodulator is necessary to receive signals; the 2-meter band lies within cable channel 18, but at 4 MHz wide, it is too narrow to fit the full 6 MHz bandwidth of an NTSC analog channel. The 2-meter band is used by ATV operators for coordination with each other via FM voice transmissions. Operators seeking an ATV contact might first attempt calling on a regionally recognized ATV liaison-frequency 144.34 MHz agree to an ATV frequency to use for the video transmissions. The 2 meter frequency may be used throughout the contact to talk back to the current station transmitting video; the receiving station may suggest adjustments the sending station can make, such as antenna direction, to improve the quality of the video received.
The 70-centimeter band is the most used ham band for ATV. Signals transmitted on this band propagate longer distances than on higher frequency bands, for a given transmitter power and antenna gain; the band falls between broadcast TV channels 13 and 14, which are 210–216 MHz and 470–476 MHz respectively. Propagation is similar to the lowest UHF TV Broadcast channels. Additionally, this band can be received by tuning any cable-ready analog television or cable-box to the cable TV channels below and connecting an outdoor TV antenna. Amateur TV signals are much weaker than broadcast TV, so a preamplifier is used to improve reception. Usage notes: In Canada and areas of the US north of a designated "Line A" boundary, amateurs are not allowed to transmit on these channels. Used as an ATV repeater output. VSB filters must be used on this channel to keep the signal inside the ham band. Channels 58 and 59 are offset in frequency to limit interference to the weak-signal and amateur radio satellite sub-bands.
Many modern CATV receivers can still lock-on to frequencies offset as much as 1 MHz. Used today due to heavy FM repeater use in this range. For technical reasons, a maximum of two channels may be used within a given geographic area, the video carrier frequencies must be at least 12 MHz apart for the signals not to interfere with each other; the 33-centimeter band is next. This ham band is unique to ITU Region 2, it is available for amateur use in ITU Regions 1 or 3; this band is shared with many users, including ISM devices and unlicensed Part 15 users, so interference issues are more than on other bands. These channels can be received by many newer analog cable-boxes and televisions, which can tune to channels above 125. Usage notes: Available, but no known usage. In portions of Colorado and Wyoming, amateurs are not allowed to transmit ATV on this channel. May interfere with growing FM use on the 927–928 MHz sub-band. For technical reasons, a maximum of two channels may be used w