Amateur television
Encyclopedia
Amateur television is the transmission of Broadcast quality
video
and audio over the wide range of frequencies of (radio wave
s) allocated for Radio amateur (Ham) use. ATV is used for non-commercial
experimentation, pleasure 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
, and PAL
or SECAM
elsewhere, utilising the full refresh rate
s of those standards. ATV includes the study of building of such transmitter
s and receivers
, and the study of radio propagation
of signals travelling between transmitting and receiving stations.
ATV is an extension of amateur radio
. It is also called HAM TV or Fast Scan TV (FSTV) (as opposed to slow-scan television
(SSTV), which can be transmitted on shortwave
ham bands due to its narrowband
structure, but is not decodable by a commercially available television receiver).
, amateur radio bands
that are suitable for a television signal (wide
enough to fit such a signal) are higher in frequency than VHF broadcast TV. The lowest frequency ham band suitable for television transmission is 70 centimeters
, which is between broadcast channels 13 and 14. While outside of broadcast television channels, this frequency falls into CATV
frequencies
, on channels 57 to 61 (420-450 MHz). As such, ATV transmissions can be viewed by setting a television to cable input and attaching an outdoor 70 cm antenna. For more sensitive reception, some users may use a purposely-built ATV down-converter, which is a kind of set-top-box. Other bands are also 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 commonly 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 (AM)
or vestigial sideband (VSB) NTSC
(North American analog TV broadcast modulation standard). AM and VSB signals are inherently compatible with each other, and most televisions can receive either. AM signals are wider than VSB signals, but VSB transmitters are more difficult and expensive to construct. For practical reasons, most individual ATV users transmit in AM, and VSB is transmitted by repeater stations. On the 33 cm and higher bands, Frequency modulation (FM)
ATV may be used, and on the SHF
and EHF
ham bands, FM is more commonly used than VSB or AM. FM ATV is incompatible with AM/VSB ATV, and a separate demodulator is necessary to receive signals.
ham band is the most used band for ATV. Signals transmitted on this band usually propagate longer distances than on high frequency bands, for a given transmitter power and antenna gain.
The 70 cm band channels (with carrier frequency
for video
and audio) are:
Usage notes:
All of these fall within the range between T.V. broadcast channels 13 and 14, which are:
ham band is next lowest frequency band available for ATV in North America. This ham band is unique to ITU Region 2, and it is rarely available for amateur use in ITU Regions 1 or 3. This band is also shared with many users, including ISM
devices and Part 15 users, so interference issues are more likely than on other bands. This is also the lowest frequency band on which FM ATV occurs. This band does fall within the CATV channel scheme; however, most current consumer equipment does not tune to channels above 125.
The 33 cm AM/VSB channels (with carrier frequency
for video
and audio) are:
Usage notes:
The 33 cm FM channels are:
ham band is the third lowest frequency band available for ATV.
Due to the wider nature of this band over the lower ones, and the expense of VSB-filters, VSB is rarely used. Most ATV is either in AM or FM. Old TVRO receivers may be used to watch FM ATV when an antenna is connected to the LNB input. The IF
of these receivers overlaps this ham band.
The 23 cm AM/VSB channels (with carrier frequency
for video
and audio) are:
Usage notes:
The 23 cm FM channels are:
Experiments with digital modes
have lagged somewhat behind those in Europe, but have taken on some new urgency given the transition of broadcast television
. WR8ATV currently has an output using DVB-S
, which is believed to be the first, and currently only, D-ATV repeater in the US.
, which generally has a narrower UHF allocation than the USA, the majority of amateur television operation is currently frequency modulated on and above. The frequencies in use depend on national permissions. In most of mainland Europe, the most common frequency is 1255MHz. Other bands commonly used for ATV are the 13cm
and 3cm bands, although ATV is used on most of the microwave bands.
In several countries cross-band repeater
s are used, with AM
inputs on 430 MHz and FM
outputs on , others have FM-ATV inputs on and outputs on .
In the United Kingdom
, much activity occurs using in-band repeater
s. These generally have an input of 1248, 1249 or 1255 MHz and typically output at 1308, 1312 or 1316 MHz, although other frequencies are also used. Simplex
operation occurs on these or other frequencies chosen to avoid interference with other users of the band, e.g. . Recent experiment
s have been done with digital
modes following widely-adopted DVB-S
and DVB-T
standards.
is used on frequencies above 1240 MHz (1.24 GHz
), where there is enough bandwidth for such wideband
transmission
s. This is often used as a repeater's input frequency
, with output being standard VSB on the four channels listed above.
In a nutshell
The quality of transmission is expressed as a "p-level"; "p" standing for "picture". P-levels range from zero to five, increasing as the picture becomes more viewable. P-0 signifies a state in which sync bars are visible, but the picture is too snowy to be seen; this occurs at a minimum signal strength of 3db. Each level represents an increase of 6db over the previous; P-5 is 30db above P-0 and represents a perfectly clear picture.
become greater, particularly at frequencies above 10 GHz. Additionally, long-distance propagation by F-layer
ionospheric skip over the horizon does not typically occur at higher frequencies, and terrain and man-made structures can affect propagation of signals, blocking or redirecting signals. Factors such as E-layer skip propagation, tropospheric enhancement
, and knife-edge diffraction
can extend the useful range of signals.
Broadcast quality
Broadcast Quality is an term stemming from quad videotape to denote the quality achieved by professional video cameras and time base correctors used for broadcast television, usually in standard definition...
video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and audio over the wide range of frequencies of (radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s) allocated for Radio amateur (Ham) use. ATV is used for non-commercial
Non-commercial
Non-commercial refers to an activity or entity that does not in some sense involve commerce, at least relative to similar activities that do have a commercial objective or emphasis...
experimentation, pleasure and public service events. Ham TV stations were on the air in many cities before commercial television
Commercial Television
Commercial Television was the third free-to-air broadcast television station in Hong Kong. It first went on air in 1975, and ceased transmissions in 1978.-History:...
stations came on the air.Various transmission standards are used, these include the broadcast transmission standards of NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
or SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
elsewhere, utilising the full refresh rate
Refresh rate
The refresh rate is the number of times in a second that a display hardware draws the data...
s of those standards. ATV includes the study of building of such transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s and receivers
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, and the study of radio propagation
Radio propagation
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
of signals travelling between transmitting and receiving stations.
ATV is an extension of amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
. It is also called HAM TV or Fast Scan TV (FSTV) (as opposed to slow-scan television
Slow-scan television
Slow-scan television is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.A technical term for SSTV is narrowband television...
(SSTV), which can be transmitted on shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
ham bands due to its narrowband
Narrowband
In radio, narrowband describes a channel in which the bandwidth of the message does not significantly exceed the channel's coherence bandwidth. It is a common misconception that narrowband refers to a channel which occupies only a "small" amount of space on the radio spectrum.The opposite of...
structure, but is not decodable by a commercially available television receiver).
North American context
In North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, amateur radio bands
Amateur radio frequency allocations
Amateur radio frequency allocation is done by national telecommunications authorities. Globally, the International Telecommunication Union oversees how much radio spectrum is set aside for amateur radio transmissions...
that are suitable for a television signal (wide
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
enough to fit such a signal) are higher in frequency than VHF broadcast TV. The lowest frequency ham band suitable for television transmission is 70 centimeters
70 centimeters
The 70-centimeter amateur radio band is a portion of the UHF radio spectrum. This band is used by amateurs engaged in emergency communications where portable and mobile radios are frequently used. Many such radios have dual-band capabilities, operating on both the 70-centimeter and 2-meter bands.-...
, which is between broadcast channels 13 and 14. While outside of broadcast television channels, this frequency falls into CATV
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
frequencies
North American cable television frequencies
In North American cable TV networks, the radio frequencies used to carry signals to the customer are allocated to standardarized channel numbers listed in the CEA standard 542. Cable channel frequencies are generally different from off-air broadcast frequencies...
, on channels 57 to 61 (420-450 MHz). As such, ATV transmissions can be viewed by setting a television to cable input and attaching an outdoor 70 cm antenna. For more sensitive reception, some users may use a purposely-built ATV down-converter, which is a kind of set-top-box. Other bands are also used for ATV, most of them in the UHF region on frequencies higher than UHF broadcast TV. 33 centimeters
33 centimeters
The 33-centimeter or 900 MHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio on a secondary basis. It ranges from 902 to 928 MHz and is unique to ITU Region 2. It is primarily used for very local communications as opposed to bands lower in frequency...
and 23 centimeters
23 centimeters
The 23 centimeter, 1200 MHz or 1.2 GHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio and amateur satellite use on a secondary basis. The amateur radio band is between 1240 MHz and 1300 MHz...
are two other commonly 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 (AM)
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
or vestigial sideband (VSB) NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
(North American analog TV broadcast modulation standard). AM and VSB signals are inherently compatible with each other, and most televisions can receive either. AM signals are wider than VSB signals, but VSB transmitters are more difficult and expensive to construct. For practical reasons, most individual ATV users transmit in AM, and VSB is transmitted by repeater stations. On the 33 cm and higher bands, Frequency modulation (FM)
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
ATV may be used, and on the SHF
Super high frequency
Super high frequency refers to radio frequencies in the range of 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from ten to one centimetres....
and EHF
Extremely high frequency
Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low infrared light, also referred to as terahertz radiation...
ham bands, FM is more commonly used than VSB or AM. FM ATV is incompatible with AM/VSB ATV, and a separate demodulator is necessary to receive signals.
70 cm band
The 70 centimeters70 centimeters
The 70-centimeter amateur radio band is a portion of the UHF radio spectrum. This band is used by amateurs engaged in emergency communications where portable and mobile radios are frequently used. Many such radios have dual-band capabilities, operating on both the 70-centimeter and 2-meter bands.-...
ham band is the most used band for ATV. Signals transmitted on this band usually propagate longer distances than on high frequency bands, for a given transmitter power and antenna gain.
The 70 cm band channels (with carrier frequency
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
for video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and audio) are:
- 57: 420-426 MHz (421.25 video, 425.75 audio)1,2
- 58: 425-431 MHz (426.25 video, 430.75 audio)1,3
- 58: 426-432 MHz (427.25 video, 431.75 audio)1
- 59: 432.75-438.75 MHz (434.00 video, 438.50 audio)3
- 59: 432-438 MHz (433.25 video, 437.75 audio)
- 60: 438-444 MHz (439.25 video, 443.75 audio)
- 61: 444-450 MHz (445.25 video, 449.75 audio)4
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.
- - Usually used as an ATV repeater output. Expensive VSB filters must be used on this channel to keep the signal inside the ham band.
- - Channels 58 and 59 are often offset in frequency to limit interference to the weak-signal and satelliteOSCAROSCAR is an acronym for Orbiting Satellite Carrying Amateur Radio. OSCAR series satellites use amateur radio frequencies to facilitate communication between amateur radio stations. These satellites can be used for free by licensed amateur radio operators for voice and data communications...
sub-bands (431-433 & 435-438 MHz respectively). Many modern CATV receivers can still lock-on to frequencies offset as much as 1 MHz. - - Rarely used today due to heavy FM repeater use in this range.
- - For technical reasons, a maximum of two channels may be simultaneously used within a given geographic area, and the video carrier frequencies must be at least 12 MHz apart for the signals not to interfere with each other.
All of these fall within the range between T.V. broadcast channels 13 and 14, which are:
- 13: 210-216 MHz (211.25 video, 215.75 audio)
- 14: 470-476 MHz (471.25 video, 475.75 audio)
33 cm band
The 33 centimeters33 centimeters
The 33-centimeter or 900 MHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio on a secondary basis. It ranges from 902 to 928 MHz and is unique to ITU Region 2. It is primarily used for very local communications as opposed to bands lower in frequency...
ham band is next lowest frequency band available for ATV in North America. This ham band is unique to ITU Region 2, and it is rarely available for amateur use in ITU Regions 1 or 3. This band is also shared with many users, including ISM
ISM band
The industrial, scientific and medical radio bands are radio bands reserved internationally for the use of radio frequency energy for industrial, scientific and medical purposes other than communications....
devices and Part 15 users, so interference issues are more likely than on other bands. This is also the lowest frequency band on which FM ATV occurs. This band does fall within the CATV channel scheme; however, most current consumer equipment does not tune to channels above 125.
The 33 cm AM/VSB channels (with carrier frequency
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
for video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and audio) are:
- 143: 906-912 MHz (907.25 video, 911.75 audio)1
- N/A: 909-915 MHz (910.25 video, 914.75 audio)
- N/A: 910-916 MHz (911.25 video, 915.75 audio)
- 144: 912-918 MHz (913.25 video, 917.75 audio)
- 145: 918-924 MHz (919.25 video, 923.75 audio)
- N/A: 922-928 MHz (923.25 video, 927.75 audio)2,3
Usage notes:
- - Available, but no known usage.
- - In portions of ColoradoColoradoColorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
and WyomingWyomingWyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, 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 simultaneously used within a given geographic area, and the video carrier frequencies must be at least 12 MHz apart for the signals not to interfere with each other.
The 33 cm FM channels are:
- 915 MHz
23 cm band
The 23 centimeters23 centimeters
The 23 centimeter, 1200 MHz or 1.2 GHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio and amateur satellite use on a secondary basis. The amateur radio band is between 1240 MHz and 1300 MHz...
ham band is the third lowest frequency band available for ATV.
Due to the wider nature of this band over the lower ones, and the expense of VSB-filters, VSB is rarely used. Most ATV is either in AM or FM. Old TVRO receivers may be used to watch FM ATV when an antenna is connected to the LNB input. The IF
Intermediate frequency
In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...
of these receivers overlaps this ham band.
The 23 cm AM/VSB channels (with carrier frequency
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
for video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and audio) are:
- 1240-1246 MHz (1241.25 video, 1245.75 audio)1
- 1252-1258 MHz (1253.25 video, 1257.75 audio)
- 1264-1270 MHz (1265.25 video, 1269.75 audio)
- 1276-1282 MHz (1277.25 video, 1281.75 audio)
- 1288-1294 MHz (1289.25 video, 1293.75 audio)
Usage notes:
- - Expensive VSB filters must be used on this channel to keep the signal inside the ham band.
- - All of the video carrier frequencies are 12 MHz apart to allow for each channel to be used simultaneously in a given geographic area without causing interference to each other.
The 23 cm FM channels are:
- 1255 MHz (Used in some areas.)
- 1265 MHz (10 MHz)
Other amateur radio bands
In addition to the above, there are other ham bands which are less commonly used for ATV:- On the 13 centimeter13 centimetersThe 13 centimeter or 2.4 GHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio and amateur satellite use on a secondary basis. The amateur radio band is between 2300 MHz and 2450 MHz...
band:- 2417.5 MHz is used for ATV links.
- 2441.5 MHz is the most used FM ATV frequency. Uses a 6.0 MHz audio sub-carrier and 4 MHz deviation.
- The 9 centimeter (3 GHz) and 5 centimeter (5 GHz)5 centimetersThe 5 centimeter or 5 GHz band is a portion of the SHF radio spectrum internationally allocated to amateur radio and amateur satellite use on a secondary basis. In ITU regions 1 and 3, the amateur radio band is between 5,650 MHz and 5,850 MHz. In ITU region 2, the amateur radio band is between...
bands have links in some areas. - On the 3 centimeter band, 10.4 GHz is a wideband FM channel and may be used as an ATV repeater input.
Other information
The distance record for ATV is between Hawaii and California on 434 MHz.http://www.hamtv.com/atvdxrecord.htmlExperiments with digital modes
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
have lagged somewhat behind those in Europe, but have taken on some new urgency given the transition of broadcast television
DTV transition in the United States
The DTV transition in the United States was the switchover from analog to exclusively digital broadcasting of free over-the-air television programming...
. WR8ATV currently has an output using DVB-S
DVB-S
DVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...
, which is believed to be the first, and currently only, D-ATV repeater in the US.
European context
In EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, which generally has a narrower UHF allocation than the USA, the majority of amateur television operation is currently frequency modulated on and above. The frequencies in use depend on national permissions. In most of mainland Europe, the most common frequency is 1255MHz. Other bands commonly used for ATV are the 13cm
13cm
13cm is a Japanese visual novel studio under Visual Art's known for creating strictly adult-oriented titles. The company has spawned two sister studios, 130cm, known for creating moe-oriented visual novels, and 13cc.-130cm:* Princess Bride...
and 3cm bands, although ATV is used on most of the microwave bands.
In several countries cross-band repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
s are used, with AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
inputs on 430 MHz and FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
outputs on , others have FM-ATV inputs on and outputs on .
In the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, much activity occurs using in-band repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
s. These generally have an input of 1248, 1249 or 1255 MHz and typically output at 1308, 1312 or 1316 MHz, although other frequencies are also used. Simplex
Simplex
In geometry, a simplex is a generalization of the notion of a triangle or tetrahedron to arbitrary dimension. Specifically, an n-simplex is an n-dimensional polytope which is the convex hull of its n + 1 vertices. For example, a 2-simplex is a triangle, a 3-simplex is a tetrahedron,...
operation occurs on these or other frequencies chosen to avoid interference with other users of the band, e.g. . Recent experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s have been done with digital
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
modes following widely-adopted DVB-S
DVB-S
DVB-S is an abbreviation for Digital Video Broadcasting — Satellite; it is the original Digital Video Broadcasting forward error coding and demodulation standard for satellite television and dates from 1994, in its first release, while development lasted from 1993 to 1997...
and DVB-T
DVB-T
DVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
standards.
Transmission characteristics
Typically frequency modulated TVTelevision
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
is used on frequencies above 1240 MHz (1.24 GHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
), where there is enough bandwidth for such wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
s. This is often used as a repeater's input frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, with output being standard VSB on the four channels listed above.
In a nutshell
- below 1.24 GHz: Vestigial Sideband
- above 1.24 GHz: FMFrequency modulationIn telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
, PSKPhase-shift keyingPhase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
etc...
The quality of transmission is expressed as a "p-level"; "p" standing for "picture". P-levels range from zero to five, increasing as the picture becomes more viewable. P-0 signifies a state in which sync bars are visible, but the picture is too snowy to be seen; this occurs at a minimum signal strength of 3db. Each level represents an increase of 6db over the previous; P-5 is 30db above P-0 and represents a perfectly clear picture.
Range
As transmission frequency increases, atmospheric path lossesPath loss
Path loss is the reduction in power density of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system....
become greater, particularly at frequencies above 10 GHz. Additionally, long-distance propagation by F-layer
F region
The F region of the ionosphere is home to the F layer of ionization, also called the Appleton layer, after the English physicist Edward Appleton. As with other ionospheric sectors, 'layer' implies a concentration of plasma, while 'region' is the area that contains the said layer...
ionospheric skip over the horizon does not typically occur at higher frequencies, and terrain and man-made structures can affect propagation of signals, blocking or redirecting signals. Factors such as E-layer skip propagation, tropospheric enhancement
Tropospheric propagation
Tropospheric propagation describes electromagnetic propagation in relation to the troposphere.The service area from a television or frequency modulated radio transmitter extends to just beyond the optical horizon, at which point signals start to rapidly reduce in strength...
, and knife-edge diffraction
Knife-edge effect
In electromagnetic wave propagation, the knife-edge effect or edge diffraction is a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building....
can extend the useful range of signals.
Content
Content produced by ATV has included:- From 1968 to about 2004 amateur TV provided behind-the-scenes co-ordination for the annual New Year's Day Tournament of Roses ParadeTournament of Roses ParadeThe Tournament of Roses Parade, better known as the Rose Parade, is "America's New Year Celebration", a festival of flower-covered floats, marching bands, equestrians and a college football game on New Year's Day , produced by the non-profit Pasadena Tournament of Roses Association.The annual...
in Pasadena, CA.
- HAM TV - as it is also called - provides video co-ordination of many public service events and, along with traditional amateur radio, provides much needed "eyes" in natural disasters.
- U.S. stations often retransmit NASA TVNASA TVNASA TV is the television service of the United States government agency NASA. NASA TV is broadcast by satellite with a simulcast over the Internet. Local cable television systems across the U.S. and amateur television repeaters may carry NASA TV at their discretion, as NASA-created content is...
while they are not in use, especially if there is currently a Space ShuttleSpace ShuttleThe Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
missionSpace explorationSpace exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....
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See also
- ATSC Standards
- DVB-TDVB-TDVB-T is an abbreviation for Digital Video Broadcasting — Terrestrial; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in the UK in 1998...
- NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
- SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
- SSTVSlow-scan televisionSlow-scan television is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.A technical term for SSTV is narrowband television...