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58-502: FT8 is a popular form of digital weak signal communication used primarily by amateur radio operators to communicate on amateur radio bands with a majority of traffic occurring on the HF amateur bands. The mode offers operators the ability to communicate despite unfavorable conditions such as during low solar activity , high RF noise, or with low transmit power . With advances in signal processing technology, software can decode FT8 signals with

116-647: A 2500 Hz bandwidth is −21 dB, so the corresponding E b / N 0 is 10 log 10 (2500/6.09) = 26.1 dB greater, or −21 dB + 26.1 = 5.1 dB. Although FT8 transmissions occur within fixed time windows, the software can cope with discrepancies between sending and receiving systems of up to a second or two. Provided that they are manually set to the correct time every so often (for example, by using WWV or other time standard broadcasters), conventional computer Real Time Clocks are usually adequate. However, most FT8 users take advantage of online time servers using NTP or time signals from

174-607: A bandwidth of less than 60 Hz. The Report and Order also allows the use of modes that comply with emission designator “2K80J2D”, which includes any digital mode with a bandwidth of 2.8 kHz or less whose technical characteristics have been documented publicly, per Part 97.309(4) of the FCC Rules. Such modes would include PACTOR  I, II, or III, 300  baud packet, MFSK , MT63 , Contestia , Olivia , DominoEX, and others. On 60 meters , hams are restricted to only one signal per channel, and automatic operation

232-700: A distance of more than 6 000 km (4 000 miles). Tropo-scatter happens when water droplets and dust particles refract a VHF or UHF signal over the horizon. Using relatively high power and a high gain antenna, this propagation will give marginal enhanced over-the-horizon VHF and UHF communications up to several hundred kilometres (miles). During the 1970s commercial "scatter site" operators using huge parabolic antennas and high power used this mode successfully for telephone communications services into northern remote Alaska and Canadian communities. Satellite, buried fibre optic, and terrestrial microwave access have relegated commercial use of tropo-scatter to

290-502: A process to move these stations to UHF bands to free up valuable VHF spectrum for its original purpose of FM radio. In addition, by 1985 the federal government decided new TV stations are to be broadcast on the UHF band. Two new VHF channels, 9A and 12, have since been made available and are being used primarily for digital services (e.g. ABC in capital cities) but also for some new analogue services in regional areas. Because channel 9A

348-669: A proposed transmitter station. VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a quarter wave whip antenna at VHF frequencies is 25 cm to 2.5 meter (10 inches to 8 feet) long. So the VHF and UHF wavelengths are used for two-way radios in vehicles, aircraft, and handheld transceivers and walkie-talkies . Portable radios usually use whips or rubber ducky antennas , while base stations usually use larger fiberglass whips or collinear arrays of vertical dipoles. For directional antennas,

406-515: A result, FM radio receivers such as those found in automobiles which are designed to tune into this frequency range could receive the audio for analog-mode programming on the local TV channel 6 while in North America. The practice largely ended with the DTV transition in 2009, although some still exist. The FM broadcast channel at 87.9 MHz is normally off-limits for FM audio broadcasting; it

464-641: A search of the ACMA Radcomms register [2] . ) The Wireless Institute of Australia has charts for Amateur frequencies for Australia . The New Zealand Association of Radio Transmitters (NZART) has charts for Amateur frequencies for New Zealand . The Japanese have charts for Amateur frequencies in Japan Radio amateurs may engage in satellite and space craft communications; however, the frequencies allowed for such activities are allocated separately from more general use radio amateur bands. Under

522-503: A signal-to-noise ratio as low as −20 dB in a 2500 Hz bandwidth, which is significantly lower than conventional CW or SSB transmissions. FT8 involves 77-bit message blocks transmitted in regular 15-second periods, consisting of 12.64 seconds of transmission time and 2.36 seconds of decode time, giving a digital data rate of 6.09 bits/sec. Source encoding gives an effective message throughput equivalent to about 5 words per minute. The required signal-to-noise ratio in

580-477: A simple antenna, range would be around 50 km (30 miles). With a large antenna system like a long yagi , and higher power (typically 100 watts or more) contacts of around 1 000 km (600 miles) using the Morse code (CW) and single-sideband (SSB) modes are common. Ham operators seek to exploit the limits of the frequencies usual characteristics looking to learn, understand, and experiment with

638-620: Is a popular club dedicated to this digital mode. The FT8 Operating Guide gives pragmatic advice on using FT8 for HF communications. Amateur radio bands Amateur radio frequency allocation is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by

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696-528: Is a radio band which, in most of the world, is used for FM broadcasting . In North America , however, this bandwidth is allocated to VHF television channel 6 (82–88 MHz). The analog audio for TV channel 6 is broadcast at 87.75 MHz (adjustable down to 87.74). Several stations, known as Frankenstations , most notably those joining the Pulse 87 franchise, have operated on this frequency as radio stations, though they use television licenses. As

754-622: Is available for use in several countries, and the 2007 World Radiocommunication Conference (WRC-07) recommended it as a worldwide amateur allocation. Before the introduction of the 2 200 metre band in the U.K. in 1998, operation on the even lower frequency of 73 kHz, in the LF time signal band, was allowed from 1996–2003. ITU Region 1 corresponds to Europe, Russia, Africa and the Middle East. For ITU region 1, Radio Society of Great Britain 's band plan will be more definitive (click on

812-708: Is called a bandplan ; it may be determined by regulation, but most typically is set by agreements between amateur radio operators. National authorities regulate amateur usage of radio bands. Some bands may not be available or may have restrictions on usage in certain countries or regions. International agreements assign amateur radio bands which differ by region. Frequencies above 30 MHz are referred to as Very High Frequency (VHF) region and those above 300 MHz are called Ultra High Frequency (UHF). The allocated bands for amateurs are many megahertz wide, allowing for high-fidelity audio transmission modes ( FM ) and very fast data transmission modes that are unfeasible for

870-558: Is less of a problem in this and higher frequency bands than at lower frequencies. The VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for two-way land mobile radio systems , such as walkie-talkies , and two way radio communication with aircraft ( Airband ) and ships ( marine radio ). Occasionally, when conditions are right, VHF waves can travel long distances by tropospheric ducting due to refraction by temperature gradients in

928-588: Is not permitted. In addition, the FCC continues to require that all digital transmissions be centred on the channel-centre frequencies, which the Report and Order defines as being 1.5 kHz above the suppressed carrier frequency of a transceiver operated in the upper side-band (USB) mode. As amateur radio equipment displays the carrier frequency, it is important for operators to understand correct frequency calculations for digital "sound-card" modes to ensure compliance with

986-517: Is not really a propagation mode, but rather an active repeater system. Satellites have been highly successful in providing VHF/UHF/SHF users "propagation" beyond the horizon. Amateurs have sponsored the launch of dozens of communications satellites since the 1970s. These satellites are usually known as OSCARs (Orbiting Satellite Carrying Amateur Radio). Also, the ISS has amateur radio repeaters and radio location services on board. Amateur television (ATV)

1044-469: Is not used for television services in or near Sydney, Melbourne, Brisbane, Adelaide or Perth, digital radio in those cities are broadcast on DAB frequencies blocks 9A, 9B and 9C. VHF radio is also used for marine Radio as per its long-distance reachability comparing UHF frequencies. Example allocation of VHF–UHF frequencies: Until 2013, the four main free-to-air TV stations in New Zealand used

1102-455: Is on the order of 270 dB for 70 cm signals. Return signals are weak and distorted because of the relative velocities of the transmitting station, Moon and the receiving station. The Moon's surface is also very rocky and irregular. Because of the weak, distorted return signals, Moon bounce communications use digital modes. For example, old-fashioned Morse code or modern JT65 , designed for working with weak signals. Satellite relay

1160-612: Is reserved for displaced class D stations which have no other frequencies in the normal 88.1–107.9 MHz subband to move to. So far, only two stations have qualified to operate on 87.9 MHz: 10–watt KSFH in Mountain View, California and 34–watt translator K200AA in Sun Valley, Nevada . In some countries, particularly the United States and Canada, limited low-power license-free operation

1218-510: Is the hobby of transmitting broadcast -compatible video and audio by amateur radio. It also includes the study and building of such transmitters and receivers and the propagation between these two. In NTSC countries, ATV operation requires the ability to use a 6 MHz wide channel. All bands at VHF or lower are less than 6 MHz wide, so ATV operation is confined to UHF and up. Bandwidth requirements will vary from this for PAL and SECAM transmissions. ATV operation in

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1276-761: The Amateur Radio Service , the Amateur Satellite Service receives its own frequency allocations. All the allocations are within amateur radio bands, and with one exception, the allocations are the same in all three ITU regions . Very High Frequency Very high frequency ( VHF ) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves ) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and

1334-456: The GPS to achieve and maintain better time accuracy, automatically. Forward error correction helps achieve reliable communication despite common RF issues such as fading and interference, and weak/noisy signals due to marginal propagation paths, low power operation and inefficient antennas (e.g. in restricted and overcrowded urban locations). If anticipated messages are missed or not acknowledged,

1392-695: The HF band there is only some reflection at lower frequencies from the ionosphere ( skywave propagation). They do not follow the contour of the Earth as ground waves and so are blocked by hills and mountains, although because they are weakly refracted (bent) by the atmosphere they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause multipath propagation , which can interfere with television reception. Atmospheric radio noise and interference ( RFI ) from electrical equipment

1450-522: The International Telecommunication Union 's rules, all amateur radio operations may only occur within 50 kilometres (31 mi) of the Earth's surface. As such, the Amateur Radio Service is not permitted to engage in satellite operations; however, a sister radio service, called the Amateur Satellite Service , exists which allows satellite operations for the same purposes as the Amateur Radio Service . In most countries, an amateur radio license conveys operating privileges in both services, and in practice,

1508-619: The Yagi antenna is the most widely used as a high gain or "beam" antenna. For television reception, the Yagi is used, as well as the log-periodic antenna due to its wider bandwidth. Helical and turnstile antennas are used for satellite communication since they employ circular polarization . For even higher gain, multiple Yagis or helicals can be mounted together to make array antennas . Vertical collinear arrays of dipoles can be used to make high gain omnidirectional antennas , in which more of

1566-417: The channelled 60 meter band is the U.S. National Telecommunications and Information Administration (NTIA). Effective 5 March 2012 the FCC permits CW, USB, and certain digital modes on these frequencies by amateurs on a secondary basis. The FCC Report and Order permits the use of digital modes that comply with emission designator “60H0J2B”, which includes PSK31 as well as any RTTY signal with

1624-410: The kilohertz -wide allocations in the HF bands. forwarding systems While "line of sight" propagation is a primary factor for range calculation, much of the interest in the bands above HF comes from use of other propagation modes. A signal transmitted on VHF from a hand-held portable will typically travel about 5–10 km (3–6 miles) depending on terrain. With a low power home station and

1682-588: The medium-wave broadcast band , but in recent times, as the historic users of these low frequencies have been vacating the spectrum, limited space has opened up to allow for new amateur radio allocations and special experimental operations. Since parts of the 500 kHz band are no longer used for regular maritime communications, some countries permit amateur radio radiotelegraph operations in that band. Many countries, however, continue to restrict these frequencies which were historically reserved for maritime and aviation distress calls. The 2 200 metre band

1740-435: The 10 VHF channels were insufficient to support the growth of television services. This was rectified by the addition of three additional frequencies-channels 0, 5A and 11. Older television sets using rotary dial tuners required adjustment to receive these new channels. Most TVs of that era were not equipped to receive these broadcasts, and so were modified at the owners' expense to be able to tune into these bands; otherwise

1798-596: The 11 year sunspot cycle. The longest terrestrial contact ever reported on 2 metres (146 MHz) was between a station in Italy and a station in South Africa, a distance of 7 784 km (4 837 miles), using trans-equatorial anomalous enhancement (TE) of the ionosphere over the geomagnetic equator. This enhancement is known as TE, or trans-equatorial propagation and (usually) occurs at latitudes 2 500–3 000 km (1500–1900 miles) within either side of

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1856-541: The 625-line colour signal), with the exception of BBC2 (which had always broadcast solely on UHF). The last British VHF TV transmitters closed down on January 3, 1985. VHF band III is now used in the UK for digital audio broadcasting , and VHF band II is used for FM radio , as it is in most of the world. Unusually, the UK has an amateur radio allocation at 4 metres , 70–70.5 MHz. Frequency assignments between US and Canadian users are closely coordinated since much of

1914-498: The 70 cm band is particularly popular, because the signals can be received on any cable-ready television. Operation in the 33 cm and 23 cm bands is easily augmented by the availability of various varieties of consumer-grade wireless video devices that exist and operate in unlicensed frequencies coincident to these bands. Repeater ATV operation requires specially-equipped repeaters. Historically, amateur stations have rarely been allowed to operate on frequencies lower than

1972-458: The Americas and many other parts of the world, VHF Band I was used for the transmission of analog television . As part of the worldwide transition to digital terrestrial television most countries require broadcasters to air television in the VHF range using digital, rather than analog encoding. Radio waves in the VHF band propagate mainly by line-of-sight and ground-bounce paths; unlike in

2030-557: The Canadian population is within VHF radio range of the US border. Certain discrete frequencies are reserved for radio astronomy . The general services in the VHF band are: Cable television , though not transmitted aerially, uses a spectrum of frequencies overlapping VHF. The U.S. FCC allocated television broadcasting to a channelized roster as early as 1938 with 19 channels. That changed three more times: in 1940 when Channel 19

2088-471: The VHF television bands ( Band I and Band III ) to transmit to New Zealand households. Other stations, including a variety of pay and regional free-to-air stations, were forced to broadcast in the UHF band, since the VHF band had been very overloaded with four stations sharing a very small frequency band, which was so overcrowded that one or more channels would not be available in some smaller towns. However, at

2146-456: The amateur satellite community for proposed satellite operating frequencies before deciding local bandplans above 1300 MHz. Not all Member Unions follow this plan. As an example, the ACMA does not allow Australian Amateurs to use 3.700 MHz to 3.768 MHz and 3.800 MHz to 3.900 MHz, allocating this region to Emergency and Ambulatory services (Allocations can be found conducting

2204-460: The antenna's power is radiated in horizontal directions. Television and FM broadcasting stations use collinear arrays of specialized dipole antennas such as batwing antennas . Certain subparts of the VHF band have the same use around the world. Some national uses are detailed below. The VHF TV band in Australia was originally allocated channels 1 to 10-with channels 2, 7 and 9 assigned for

2262-427: The atmosphere. VHF transmission range is a function of transmitter power, receiver sensitivity, and distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight phenomenon. The distance to the radio horizon is slightly extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere. An approximation to calculate

2320-464: The boundaries of these warm/cold atmospheric layers. Radio signals have been known to travel hundreds, even thousands of kilometres (miles) due to these unique weather conditions. For example: The longest distance reported contact due to tropospheric refraction on 2 metres is 4 754 km (2 954 miles) between Hawaii and a ship south of Mexico . There were reports of the reception of one way signals from Réunion to Western Australia ,

2378-549: The buttons at the bottom of the page). The following charts show the voluntary bandplans used by amateurs in ITU Region ;1. Unlike the US, slots for the various transmission modes are not set by the amateur's license but most users do follow these guidelines. ITU Region 2 consists of the Americas, including Greenland. The frequency allocations for hams in ITU Region 2 are: The primary (first priority) user of

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2436-637: The channel-center requirement. The ARRL has a "detailed band plan" for US hams showing allocations within each band. RAC has a "chart showing the frequencies available to amateurs in Canada" . 21 June 2017 . Canadian operators are restricted to 100 watts PEP. ITU region 3 consists of Australia, Indonesia, Japan, New Zealand, the South Pacific, and Asia south of Siberia. The IARU frequency allocations for hams in ITU Region 3 are: Bands above 1300 MHz: societies should consult with

2494-504: The class of the station license. Radio amateurs use a variety of transmission modes, including Morse code , radioteletype , data, and voice. Specific frequency allocations vary from country to country and between ITU regions as specified in the current ITU HF frequency allocations for amateur radio. The list of frequency ranges is called a band allocation , which may be set by international agreements, and national regulations. The modes and types of allocations within each frequency band

2552-473: The end of 2013 , all television channels stopped broadcasting on the VHF bands, as New Zealand moved to digital television broadcasting, requiring all stations to either broadcast on UHF or satellite (where UHF was unavailable) utilising the Freeview service. Refer to Australasian television frequencies for more information. British television originally used VHF band I and band III . Television on VHF

2610-414: The equator. An intense solar storm causing aurora borealis (northern lights) will also provide occasional propagation enhancement to HF-low (6-metre) band radio waves. Aurorae only occasionally affect signals on the 2 metre band . Signals are often distorted and on the lower frequencies give a curious "watery sound" to normally propagated HF signals. Peak signals usually come from the north, even if

2668-403: The history books. Because of high cost and complexity this mode is usually out of reach for the average amateur radio operator. F2 and TE band openings from other ionospheric reflection/refraction modes, or sky-wave propagation as it is known can also occasionally occur on the low band VHF frequencies of 6 or 4 metres, and very rarely on 2 metres (high band VHF) during extreme peaks in

2726-565: The initial services in Sydney and Melbourne , and later the same channels were assigned in Brisbane , Adelaide and Perth . Other capital cities and regional areas used a combination of these and other frequencies as available. The initial commercial services in Hobart and Darwin were respectively allocated channels 6 and 8 rather than 7 or 9. By the early 1960s it became apparent that

2784-481: The legal distinction between the two services is transparent to the average licensee. The primary reason the two services are separate is to limit the frequencies available for satellite operations. Due to the shared nature of the amateur radio allocations internationally, and the nature of satellites to roam worldwide, the ITU does not consider all amateur radio bands appropriate for satellite operations. Being separate from

2842-408: The line-of-sight horizon distance (on Earth) is: These approximations are only valid for antennas at heights that are small compared to the radius of the Earth. They may not necessarily be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves. In engineered communications systems, more complex calculations are required to assess the probable coverage area of

2900-826: The next higher frequencies are known as ultra high frequency (UHF). VHF radio waves propagate mainly by line-of-sight , so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting , two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems , amateur radio , and marine communications . Air traffic control communications and air navigation systems (e.g. VOR and ILS ) work at distances of 100 kilometres (62 miles) or more to aircraft at cruising altitude. In

2958-574: The owner had to buy a new TV. Several TV stations were allocated to VHF channels 3, 4 and 5, which were within the FM radio bands although not yet used for that purpose. A couple of notable examples were NBN-3 Newcastle , WIN-4 Wollongong and ABC Newcastle on channel 5. While some Channel 5 stations were moved to 5A in the 1970s and 80s, beginning in the 1990s, the Australian Broadcasting Authority began

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3016-784: The possibilities of these enhanced propagation modes. Occasionally, several different ionospheric conditions allow signals to travel beyond the ordinary line-of-sight limits. Some amateurs on VHF seek to take advantage of "band openings" where natural occurrences in the atmosphere and ionosphere extend radio transmission distances well over their normal range. Many hams listen for hours hoping to take advantage of these occasional extended propagation "openings". The ionospheric conditions are called sporadic E and anomalous enhancement . Less frequently used anomalous modes are tropospheric scatter and Aurora Borealis (Northern Lights). Moon bounce and satellite relay are also possible. Some openings are caused by islands of intense ionization of

3074-477: The signal originates from a station to the east or west of the receiver. This effect is most significant in the latitudes north of 45 degrees. Amateurs do successfully communicate by bouncing their signals off the surface of the Moon, called Earth-Moon-Earth (EME) transmission. The mode requires moderately high power (more than 500 watts) and a fairly large, high-gain antenna because round-trip path loss

3132-745: The software can re-send them in the next time-slot. The 77 bits are sufficient for free text messages of up to 13 text characters, reminiscent of SMS (TXT) messages or Tweets , while a clever data compression scheme reduces the number of digital bits required to pass structured messages containing conventional callsigns, reports and locators. Long or unusual callsigns are problematic for the protocol, however, despite using hashing to pass condensed representations. Decoding errors and hash collisions occasionally generate false 'callsigns' creating puzzlement or excitement if they appear to be rare but genuine calls. There are multiple uses for FT8 including contesting, testing antennas, and for scientific research. FT8DMC

3190-459: The spring and early summer months. This phenomenon occurs during the fall months, although not as often. Band openings are sometimes caused by a weather phenomenon known as a tropospheric "inversion" , where a stagnant high pressure area causes alternating stratified layers of warm and cold air generally trapping the colder air beneath. This may make for smoggy or foggy days, but it also causes VHF and UHF radio transmissions to travel or duct along

3248-525: The upper atmosphere, known as the E ;Layer ionosphere . These islands of intense ionization are called " sporadic E " and result in erratic but often strong propagation characteristics on the "low[er] band" VHF radio frequencies. The 6 metre amateur band falls into this category, often called "the magic band", will often "open up" from one small area into another small geographic area 1 000–1 700 km (600–1 000 miles) away during

3306-406: Was deleted and several channels changed frequencies, then in 1946 with television going from 18 channels to 13 channels, again with different frequencies, and finally in 1948 with the removal of Channel 1 (analog channels 2–13 remain as they were, even on cable television ). Channels 14–19 later appeared on the UHF band, while channel 1 remains unused. 87.5–87.9 MHz

3364-399: Was in black and white with 405-line format (although there were experiments with all three colour systems- NTSC , PAL , and SECAM -adapted for the 405-line system in the late 1950s and early 1960s). British colour television was broadcast on UHF (channels 21–69), beginning in the late 1960s. From then on, TV was broadcast on both VHF and UHF (VHF being a monochromatic downconversion from

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