Power amplifier classes
Power amplifier classes are, in electronics, letter symbols applied to different power amplifier types. The class gives a broad indication of performance; the classes are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input. A class A amplifier is conducting through all the period of the signal. A Class D amplifier operates its output device in a switching manner. Additional letter classes are defined for special purpose amplifiers, with additional active elements or particular power supply improvements. Power amplifier circuits are classified as A, B, AB and C for analog designs—and class D and E for switching designs; the classes are based on the proportion of each input cycle during which an amplifying device passes current. The image of the conduction angle derives from amplifying a sinusoidal signal. If the device is always on, the conducting angle is 360°. If it is on for only half of each cycle, the angle is 180°.
The angle of flow is related to the amplifier power efficiency. In the illustrations below, a bipolar junction transistor is shown as the amplifying device; however the same attributes are found with MOSFETs or vacuum tubes. In a Class A amplifier, 100% of the input signal is used; the active element remains conducting all of the time. Amplifying devices operating in class A conduct over the entire range of the input cycle. A class-A amplifier is distinguished by the output stage devices being biased for class A operation. Subclass A2 is sometimes used to refer to vacuum-tube class-A stages that drive the grid positive on signal peaks for more power than normal class A. This, incurs higher signal distortion. Class-A designs can be simpler than other classes insofar as class -AB and -B designs require two connected devices in the circuit, each to handle one half of the waveform whereas class A can use a single device; the amplifying element is biased so the device is always conducting, the quiescent collector current is close to the most linear portion of its transconductance curve.
Because the device is never'off' there is no "turn on" time, no problems with charge storage, better high frequency performance and feedback loop stability. The point where the device comes closest to being'off' is not at'zero signal', so the problems of crossover distortion associated with class-AB and -B designs is avoided. Best for low signal levels of radio receivers due to low distortion. Class-A amplifiers are inefficient. A maximum theoretical efficiency of 25% is obtainable using usual configurations, but 50% is the maximum for a transformer or inductively coupled configuration. In a power amplifier, this not only wastes power and limits operation with batteries, but increases operating costs and requires higher-rated output devices. Inefficiency comes from the standing current that must be half the maximum output current, a large part of the power supply voltage is present across the output device at low signal levels. If high output power is needed from a class-A circuit, the power supply and accompanying heat becomes significant.
For every watt delivered to the load, the amplifier itself, at best, uses an extra watt. For high power amplifiers this means large and expensive power supplies and heat sinks; because the output tubes are in full operation at all times, the tubes will not have as long a life, adding to the cost of maintaining the amplifier. Class-A power amplifier designs have been superseded by more efficient designs, though their simplicity makes them popular with some hobbyists. There is a market for expensive high fidelity class-A amps considered a "cult item" among audiophiles for their absence of crossover distortion and reduced odd-harmonic and high-order harmonic distortion. Class A power amps are used in some "boutique" guitar amplifiers due to their unique tonal quality and for reproducing vintage tones; some hobbyists who prefer class-A amplifiers prefer the use of thermionic valve designs instead of transistors, for several reasons: Single-ended output stages have an asymmetrical transfer function, meaning that even-order harmonics in the created distortion tend to not cancel out.
For tubes, or FETs, most distortion is second-order harmonics, from the square law transfer characteristic, which to some produces a "warmer" and more pleasant sound. For those who prefer low distortion figures, the use of tubes with class A together with symmetrical circuits results in the cancellation of most of the distortion harmonics, hence the removal of most of the distortion. Valve amplifiers were used as a class-A power amplifier because valves are large and expensive. Transistors are much less expensive than tubes so more elaborate designs that use more parts are still less expensive to manufacture than tube designs. A classic application for a pair of class-A devices is the long-tailed
Digital audio broadcasting
Digital audio broadcasting is a digital radio standard for broadcasting digital audio radio services, used in many countries around the world, though not North America. The DAB standard was initiated as a European research project in the 1980s; the Norwegian Broadcasting Corporation launched the first DAB channel in the world on 1 June 1995, the BBC and Swedish Radio launched their first DAB digital radio broadcasts in September 1995. DAB receivers have been available in many countries since the end of the 1990s. DAB is more efficient in its use of spectrum than analogue FM radio, thus can offer more radio services for the same given bandwidth; however the sound quality can be noticeably inferior if the bit-rate allocated to each audio program is not sufficient. DAB is more robust with regard to noise and multipath fading for mobile listening, although DAB reception quality degrades when the signal strength falls below a critical threshold, whereas FM reception quality degrades with the decreasing signal, providing effective coverage over a larger area.
The original version of DAB used the MP2 audio codec. An upgraded version of the system was released in February 2007, called DAB+, which uses the HE-AAC v2 audio codec. DAB is not forward compatible with DAB+, which means that DAB-only receivers are not able to receive DAB+ broadcasts. However, broadcasters can mix DAB and DAB+ programs inside the same transmission and so make a progressive transition to DAB+. DAB+ is twice as efficient as DAB, more robust. In spectrum management, the bands that are allocated for public DAB services, are abbreviated with T-DAB, where the "T" stands for terrestrial; as of 2018, 41 countries are running DAB services. The majority of these services are using DAB+, with only Ireland, UK, New Zealand and Brunei still using a significant number of DAB services. See Countries using DAB/DMB. In many countries, it is expected that existing FM services will switch over to DAB+. Norway is the first country to implement a national FM radio analog switchoff, in 2017, however that only applied to national broadcasters, not local ones.
DAB has been under development since 1981 at the Institut für Rundfunktechnik. The first DAB demonstrations were held in 1985 at the WARC-ORB in Geneva, in 1988 the first DAB transmissions were made in Germany. DAB was developed as a research project for the European Union, which started in 1987 on initiative by a consortium formed in 1986; the MPEG-1 Audio Layer II codec was created as part of the EU147 project. DAB was the first standard based on orthogonal frequency division multiplexing modulation technique, which since has become one of the most popular transmission schemes for modern wideband digital communication systems. A choice of audio codec and error-correction coding schemes and first trial broadcasts were made in 1990. Public demonstrations were made in 1993 in the United Kingdom; the protocol specification was finalized in 1993 and adopted by the ITU-R standardization body in 1994, the European community in 1995 and by ETSI in 1997. Pilot broadcasts were launched in several countries in 1995.
In October 2005, the World DMB Forum instructed its Technical Committee to carry out the work needed to adopt the AAC+ audio codec and stronger error correction coding. This work led to the launch of the DAB+ system. By 2006, 500 million people worldwide were in the coverage area of DAB broadcasts, although by this time sales of receivers had only taken off in the United Kingdom and Denmark. In 2006 there were 1,000 DAB stations in operation worldwide; as of 2018, over 68 million devices have been sold worldwide, over 2,270 DAB services are on air. DAB uses a wide-bandwidth broadcast technology and spectra have been allocated for it in Band III and L band, although the scheme allows for operation between 30 and 300 MHz; the US military has reserved L-Band in the USA only, blocking its use for other purposes in America, the United States has reached an agreement with Canada to restrict L-Band DAB to terrestrial broadcast to avoid interference. DAB had a number of country specific transmission modes.
Mode I for Band III, Earth Mode II for L-Band and satellite Mode III for frequencies below 3 GHz, Earth and satellite Mode IV for L-Band and satelliteIn January 2017, an updated DAB specification removed Modes II, III and IV, leaving only Mode I. From an OSI model protocol stack viewpoint, the technologies used on DAB inhabit the following layers: the audio codec inhabits the presentation layer. Below, the data link layer, in charge of statistical time division multiplexing and frame synchronization; the physical layer contains the error-correction coding, OFDM modulation, dealing with the over-the-air transmission and reception of data. Some aspects of these are described below. DAB uses the MPEG-1 Audio Layer II audio codec, referred to as MP2 because of the ubiquitous MP3; the newer DAB+ standard adopted the HE-AAC version 2 audio codec known as'AAC+' or'aacPlus'. AAC+ is three times more efficient than MP2, which means that broadcasters using DAB+ are able to provide far higher audio quality or far more stations than they could with DAB, or a combination of both higher audio quality and more stations.
One of the most important decisions regarding the design of a digital radio broadcasting system is the choice of which audio codec to use, because the efficiency of the audio codec determines how many radio stations can be carried on a fixed capacity multiplex at a given level of audio quality. Error-correction coding is an import
Bald Hills Radiator
Bald Hill Radiator is a radio transmission centre at 99 Kluver St, Bald Hills, City of Brisbane, Australia. It is known as the National Broadcasting Service Radio Transmission Centre, it is listed on the Brisbane Heritage Register. The centre transmits all the Brisbane AM radio programmes of the Australian Broadcasting Corporation. Radio transmission was from within the Brisbane city centre; the first transmitter for radio station 4QG was located in an inner courtyard in the Executive Building in the Brisbane city centre. Operated by the Queensland Government, it started transmitting in 1925. A more powerful transmitter replaced it in 1926, on the eighth floor of the new State Government Insurance Building at the corner of George and Elizabeth Streets; the involvement of the Australian Broadcasting Commission started in 1930, with the Postmaster General's Department being responsible for technical operation. Major modifications were made to the transmitter during the ABC's use of the transmitter.
In 1935, a survey team from the Postmaster General Research Laboratories in Melbourne selected the Bald Hills site a farm, as a future location for a high-powered transmitter for 4QG, but no land acquisition occurred at that time. At that stage radio station 4QG had been in existence for ten years, the National Broadcasting Service for five years. Radio station 4QR was opened in 1938, with transmission from the roof of the Central Automatic Exchange Building in Elizabeth Street. At the start of World War II, Brisbane's skyline was dominated by five high aerial towers, of which two served 4QG and one 4QR. A further two towers served commercial stations. Land acquisitions for the current Bald Hills site commenced in 1940; the first aerial was erected on the site in 1941. The transmitter building was made of brick with a fibro roof, it was built by Thomas Frederick of Days Road, under a contract awarded in July 1941, work had started by October 1941. The farm buildings were removed at about this time.
In March 1942 General Douglas MacArthur arrived in Australia to be appointed supreme commander of the Allied Forces in the South-West Pacific. The AMP Building in Queen Street, was chosen for MacArthur's headquarters because of its central location and reinforced concrete roof, it was feared that the presence of all these high aeril towers would act as a navigational aid for Japanese aircraft seeking to attack MacArthur's headquarters. This accelerated the need to shift the transmitters out of the city centre; the first transmission from the Bald Hills site was of 4QR, on 24 March 1942, using the transmitter moved the previous night from the Central Telephone Exchange in the city. In April 1942, the 4QG transmitter was relocated to Bald Hills but not to this site but to another Bald Hills site leased from the commercial station 4BH. Known as Fischle's Jam Factory, the 4BH site was at Roghan Road near Neville Road, next to Fischle's. Bald Hills residents of the time were not impressed by this transfer of risk of Japanese attack to their area.
As the Queensland segment of the National Broadcasting Service was restricted to Brisbane and Townsville, it was proposed to use high frequency transmission to give some cover to the rest of Queensland. VLQ first went to air on 17 February 1943, transmitted by STCA880A. Land acquisitions for the present site continued through to July 1943 when the Australian Government resumed the 114 acre property from J W Guy; the transmitter building was extended in 1945-46. After World War II had ended, the existing vertical radiator was erected in 1947; the building was further extended 1962 and has been internally modified at least twice when equipment was upgraded, once in 1968 and again in about 1994. In two stages, there were minor reductions in the land holding of the site, for road widening and subdivisional redevelopment; the current area of the site is 43ha. The National Broadcasting Service Radio Transmission Centre is an 43 hectares site at 99 Kluver Street on the corner of Bracken Ridge Road, Bald Hills, facing west into Kluver Street and bounded by Taragon Street in the south and Hoyland Street in the east.
The VLQ STCA880A transmitter is a early model high powered high frequency transmitter. It is built from old technology, its design and construction pre-dating both the transistor and the silicon chip. Relying on large glass and metal radio valves, the final amplifier valves requiring a water cooling system, the transmitter in operation presented a awesome appearance when in operation, supplemented by a sound effect as the cooling system pump and fan operated. In a paper presented to the Institution of Engineers, Australia shortly before his death, Sanderson wrote:"These early units with prolific meters and open mesh panels, behind which the large glass transmitting valves glowed cherry red, contrasting with the strange blue pulsating plasmas of the mercury vapour rectifiers, had a personality and character, lacking in the sterile steel boxes, the state of the art complex non repairable transmitters of the 90s."Particular qualities of the STCA880A are its robustness and its reliability, evidenced by the decades of high quality service it gave before it was retired because the valves vital for its operation went out of production.
It was in either full-time or reserve service for forty five year
RNZ National Radio New Zealand National, known until 2007 as National Radio, is a publicly funded non-commercial New Zealand English-language radio network operated by Radio New Zealand. It specialises in programmes dedicated to news, the arts and New Zealand culture including some material in the Māori language; the programme was broadcast on the "YA" stations 1YA, 2YA, 3YA and 4YA in the main centres. In 2013, RNZ National had a 10.3 per cent market share, the highest nationwide and up from 9.1 per cent in 2009. Market share peaked at 11.1 per cent in 2011 due to the station's coverage of the Christchurch earthquake. 493,000 people listen to RNZ National over the course of a week – the second-largest cumulative audience. Its sister station is RNZ Concert. National's weekday output between 06:00 and midnight is characterized by the alternation of three extended news and current-affairs sequences and three magazine-style programmes on various topics, each of which lasts for three to five hours.
News updates are read live on the hour, by a continuity announcer outside these times. Polling by Radio New Zealand suggests Morning Report, Nine to Noon, The Panel, Nights, Saturday Morning and Sunday Morning have larger audiences than any other programme in their timeslot. Morning Report is RNZ National's long-running flagship breakfast programme, it has aired in the 06:00 to 09:00 weekday timeslot since its premiere in April 1975, has broadcast longer programmes following major events like the September 11 attacks. The programme consists of half-hourly news and weather updates, quarter-hourly headlines, voice reports and specialist bulletins, it has an estimated 349,000 listeners. The programme broadcasts for eleven months of every year. Sports, rural and Māori news bulletin air in the programme's further half-hour. Local newspaper headlines, traffic updates and business news air after 6.30, more traffic updates and newspaper headlines air after 7.30. Additional business and Māori news air the programme's final hour.
Co-hosts Guyon Espiner and Susie Ferguson interview news-makers and reporters, introduce voice reports from local staff, the BBC, the ABC and other international affiliates. The station's famous "bird calls" of distinctive native New Zealand birds end the show at 09.00. Nine to Noon is a three-hour programme of interviews with newsmakers, writers, comedians, experts and others; the programme is hosted by Kathryn Ryan. The first hour of the programme features three long-form current affairs interviews, music and a foreign correspondent; the second hour includes a freelance book reviewer and a book reading. Prime Minister Helen Clark and former Green Party MP Sue Bradford announced their resignation on the programme; the final hour includes topical expert and a reviewer. Regular contributors include John Hawkesby, Nigel Latta, Joseph Ramanos, Rod Oram, Simon Wilson, Te Radar and Michele A'Court. Since January 2009, Nine to Noon has been replaced for a one-month Christmas and summer break by Summer Noelle, a similar format magazine programme presented by Noelle McCarthy up until 2011.
The programme includes interviews with newsmakers, scientists, celebrity commentators and actors, live in-studio performances by bands and artists, musical selections. The timeslot featured The Best of Nine to Noon. Radio New Zealand's Midday Report is an hour-long series of bulletins, it includes a six-minute general news bulletin, nine-minute further news bulletin, two-minute long-range weather forecast, ten-minute business bulletin, three-minute sports bulletin, eight-minute rural bulletin and sixteen-minute world news bulletin. Local voice reports and reports from BBC, ABC and other international affiliates feature heavily. On public holidays and summer holidays, a half-hour programme includes news and world news. National's magazine-style afternoon programme is hosted by Jesse Milligan. Previous and substitute hosts have included Jim Mora, Noelle McCarthy, Finlay MacDonald, Paul Brennan, Chris Whitta and Simon Mercep, it is broadcast from Radio New Zealand's Auckland studios, includes features like The Best Song Ever Written, Reeling in the Years, Your Call New Zealand, science interviews and a live performance segment called New Zealand Live.
On public holidays and over the one-month Christmas and summer break, Kelle Howson, Phil O'Brien and Simon Morris present music variety programme Matinee Idle in the afternoon slot. It includes a large component of audience comments and recommendations, as well as a daily theme hour. In Touch with New Zealand with Wayne Mowat aired in the afternoon slot. John Campbell presents RNZ National's flagship drive time news programme, Checkpoint from Auckland's studios and it is streamed live on Radio New Zealand's website, it includes live interviews with newsmakers and correspondents on national and international news stories, as well as half-hourly news and weather updates and daily specialist segments. First broadcast in 1967, the programme is the longest-running news broadcast on radio or television in New Zealand; the programme includes six-minute news bulletins on the hour and six minute news and sports bulletins on the half hour. The first hour has a greater emphasis on domestic issues, the second hour has more of an international focus and the progr
ABC Classic is a classical music radio station available in Australia and internationally. Its website features classical music news and listening guides, it is operated by the Australian Broadcasting Corporation. ABC Classic was established in 1976 as "ABC-FM", for a short time was known as "ABC Fine Music", it became known as ABC Classic FM in 1994, before adopting its current name in January 2019. It was the ABC's first experiment in FM broadcasting – which had become a necessity in Australia as broadcasters ran out of AM frequencies on which to transmit. ABC Classic FM was inspired by the example of BBC Radio 3. ABC Classic FM's studios were established at the ABC studios in Collinswood, a suburb of Adelaide, South Australia; the ABC's decision to establish ABC Classic FM in Adelaide was significant because most of the ABC's radio and television national program origination infrastructure is located in Sydney. ABC Classic broadcasts classical music, operas and live concerts. Live music is a major feature of ABC Classic schedule.
Concerts are broadcast from around Australia and Internationally, via the European Broadcasting Union. Since 2001, ABC Classic FM has organised a number of Classic 100 Countdown surveys; the results of each survey are decided by votes cast by the listeners of the radio station. The works are broadcast in reverse order of popularity over three days; the countdown culminates in the broadcast of a live concert featuring the most popular pieces and finishes with the number one listener choice. A feature of the countdown is; each November on ABC Classic is Australian music month, where Australian artists are promoted. This includes more Australian composition broadcast every day. ABC Classic has long featured contemporary music from Australia and internationally, in part through its specialty programs New Music Australia and New Music Up Late, through its long-standing ties to the European Broadcasting Union, its ongoing podcasts and many live or studio recordings. In common with all ABC Radio stations, it carries news bulletins produced by ABC News.
On 19 December 2005, in line with the policy applied at every ABC Radio network, these news bulletins became state-based rather than national. ABC Classic 2, a music-only talk-free streaming station, was established in June 2014, it is available on the ABC's Android and iOS apps. Classic 2 specialises in streaming popular styles of classical music; the music on Classic 2 is performed by leading Australian orchestras and soloists. No opera or vocal works are included in the playlist. During daytime and evenings Classic 2 broadcasts short excerpts from the classical repertoire, for example single movements from full symphonies. Between midnight and 06:00, longer works are included. ABC Classic 2 is programmed by the ABC Classic FM team. On 24 November 2018, the ABC announced that ABC Classic FM would undergo a major rebrand in 2019, change its name to ABC Classic; the monthly arts magazine Limelight was, under its former name ABC Radio 24 Hours owned and published by the ABC. It is now independently owned and published, but continues a strong, albeit unofficial, affiliation with the ABC and with ABC Classic in particular.
Australian Broadcasting Corporation Symphony Australia Official website ABC Classic FM program guide ABC Classic FM frequencies
Hobart is the capital and most populous city of the Australian island state of Tasmania. With a population of 225,000, it is the least populated Australian state capital city, second smallest if territories are taken into account. Founded in 1804 as a British penal colony, Hobart known as Hobart Town or Hobarton, is Australia's second oldest capital city after Sydney, New South Wales. Prior to British settlement, the Hobart area had been occupied for as long as 35,000 years, by the semi-nomadic Mouheneener tribe, a sub-group of the Nuennone, or South-East tribe; the descendants of these Aboriginal Tasmanians refer to themselves as'Palawa'. Since its foundation as a colonial outpost, the city has expanded from the mouth of Sullivans Cove in a north-south direction along both banks of the Derwent River, from 22 km inland from the estuary at Storm Bay to the point where the river reverts to fresh water at Bridgewater. Penal transportation ended in the 1850s, after which the city experienced periods of growth and decline.
The early 20th century saw an economic boom on the back of mining and other primary industries, the loss of men who served in the world wars was counteracted by an influx of immigration. Despite the rise in migration from Asia and other non-English speaking parts of the world, Hobart's population remains predominantly ethnically Anglo-Celtic, has the highest percentage of Australian-born residents among the Australian capital cities. In June 2016, the estimated greater area population was 224,462; the city is located in the state's south-east on the estuary of the Derwent River, making it the most southern of Australia's capital cities. Its harbour forms the second-deepest natural port in the world, its skyline is dominated by the 1,271-metre kunanyi/Mount Wellington, much of the city's waterfront consists of reclaimed land. It is the financial and administrative heart of Tasmania, serving as the home port for both Australian and French Antarctic operations and acting as a major tourist hub, with over 1.192 million visitors in 2011/2012.
The metropolitan area is referred to as Greater Hobart, to differentiate it from the City of Hobart, one of the five local government areas that cover the city. The first European settlement began in 1803 as a military camp at Risdon Cove on the eastern shores of the Derwent River, amid British concerns over the presence of French explorers. In 1804, along with the military and convicts from the abandoned Port Phillip settlement, the camp at Risdon Cove was moved by Captain David Collins to a better location at the present site of Hobart at Sullivans Cove; the city known as Hobart Town or Hobarton, was named after Lord Hobart, the British secretary of state for war and the colonies. The area's indigenous inhabitants were members of the semi-nomadic Mouheneener tribe. Violent conflict with the European settlers, the effects of diseases brought by them reduced the aboriginal population, replaced by free settlers and the convict population. Charles Darwin visited Hobart Town in February 1836 as part of the Beagle expedition.
He writes of Hobart and the Derwent estuary in his Voyage of the Beagle:... The lower parts of the hills which skirt the bay are cleared. I was chiefly built or building. Hobart Town, from the census of 1835, contained 13,826 inhabitants, the whole of Tasmania 36,505; the Derwent River was one of Australia's finest deepwater ports and was the centre of the Southern Ocean whaling and sealing trades. The settlement grew into a major port, with allied industries such as shipbuilding. Hobart Town became a city on 21 August 1842, was renamed Hobart from the beginning of 1881. Hobart is located on the estuary of the Derwent River in the state's south-east. Geologically Hobart is built predominantly on Jurassic dolerite around the foothills interspersed with smaller areas of Triassic siltstone and Permian mudstone. Hobart extends along both sides of the Derwent River. Both of these areas rest on the younger Jurassic dolerite deposits, before stretching into the lower areas such as the beaches of Sandy Bay in the south, in the Derwent estuary.
South of the Derwent estuary lies the Tasman Peninsula. The Eastern Shore extends from the Derwent valley area in a southerly direction hugging the Meehan Range in the east before sprawling into flatter land in suburbs such as Bellerive; these flatter areas of the eastern shore rest on far younger deposits from the Quaternary. From there the city extends in an easterly direction through the Meehan Range into the hilly areas of Rokeby and Oakdowns, before reaching into the tidal flatland area of Lauderdale. Hobart has access to a number of beach areas including those in the Derwent estuary itself. Hobart has a mild temperate oceanic climate; the highest temperature recorded was 41.8 °C on 4 January 2013 and the lowest was −2.8 °C on 25 June 1972 and 11 July 1981. Annually, Hobart receives 40.8 clear days. Compared to other major Australian cities, Hobart has the fewest daily average hours of sunshine, with 5.9 hours per day. However, during the summer it has the most