In 1800, pre-history
End of the 19th century for the rapid development of commercial radio and the establishment of amateur radio provides a basis for the stage, where there are a large number of contributors to the early radio technology, such as the great Oster, Ampere, Faraday, Henry, and so on. However, it is a real turning point in 1873 the Scots JC Maxwell (not described in this article) the controversial work, he put forward the theory of electromagnetic fields, that is to be late and beloved around the globe, the founder of the distinguished equation. (Heaviside on the Maxwell equation has made a greater contribution, but that's another story.)
1920s - found that the times
As the country entered the 1920s, fans in section 200 UHF camped on. League of American radio network have been working to break the record, the most impressive in early 1921, there is a message by Connecticut 1AW Hiram Precy Maxim spread to California, 6JD VM Bitz, 6.5 minutes later received a call back , A round-trip loop.
Just a few years, predicted that the number of fans in the amateur radio in the revolutionary changes to be true. If some people have pointed out that the need to change the most important reason, it is accompanied by tube, as well as fans of the never-ending pursuit of new things.
By the age of 20, the tube prices began to fall, making use of renewable Armstrong sensitive receiver circuit design into the climax of the sparks led to the development of radio transmission enhanced the scope of this technology can not be detected in the original testing of a weak letter. Some high-level fans of Armstrong and the French during the war Lucien Levy invented superheterodyne receiver experiment. More and more fans in their transceiver in the use of electron tubes, have a balanced continuous wave signal (CW), CW narrow-band signal, only a little spark of 1% of the signal, reducing the interference, an increase of at the same time Internal air at the same time the number of work stations.
With the amateur radio station to increase the scope of the launch, DX - long-distance communication became a reality. 1921 was the other side of the Atlantic mail experiment to see if a low-power amateur radio signal can pass through the Atlantic Ocean. The ultimate experiment confirmed the feasibility of radio waves across the Atlantic, at the same time last CW shows such as the reported increase more than the superiority of words. To 1923, Europe and North America only Communications between the rest of the time. After careful preparation and hard work, in the final on November 27, 1923 in France and the United States 8AB radio Connecticut fans Fred Schnell, 1MO and John Reinartz, 1XAL particularly in authorizing the use of the segment with 110 UHF CW successful The contact. Experiment lasted until the latter part of 1924, the United Kingdom and New Zealand between the fans also had a successful communication, almost half of the around the world. In 1926, Brandon Wentworth, 6OI use in California and Stanford University on the lawn of the radio and almost all of the mainland and radio contact had been confirmed, is known as DX-distance communications authority. The following year they appeared in Insein not changed as of the ARRL DX-contest international long-distance communications of the former race-ARRL Amateur Radio Union dissemination.
In the mid-20, amateur radio enthusiasts to own a large number of measurements, the value of the short-wave is completely by the government and commercial entities recognized. At the end of the 1920s, the band of open space era has gone forever, and amateur radio enthusiasts have been adjusted to 169 meters above the 5 wave plus narrow 400MHz.
20 years on behalf of the two events worth mentioning: the first thing on behalf of the worldwide amateur radio group set up by the International Amateur Radio Amateur Radio Union (IARL). IARU still has a single-minded representatives of international organizations, the radio. The second is due to the control of the Ministry of Commerce of the United States caused chaos in the broadcasting industry, Congress in 1927 passed the bill and set up a radio FRC - Federal Radio Commission.
1930's of the twentieth century - growth
Amateur radio into the 1930s, radio has become a spark in the past, all the fans use the tube transceiver, if not universal, and other pieces of newspaper, but has gradually popular. In a few years ago, Japan Research Professor Hidetsugu Yagi dipole antenna array for microwave directional spread. To the 1930s, which was designed to use short-wave, the number of fans with this new invention YAGI antenna (that Yagi antenna) to carry out experiments, they used wire and metal components, but often with a wooden scaffold support. Some of the wealth of technology enthusiasts continue to 5 meters and higher-band communications test done.
ARRL tournament prize was founded in 1930, in 1933 established the ARRL "Outdoor Day", and the ARRL DX game is still the most popular long-distance communication game enthusiasts.
Almost no attention at the same time, Robert M. Moore, W6DEI in September 1933 and October in Los Angeles, published by the three parts of the composition of the "R / 9" magazine, published on the "Amateur radio telephone unilateral With the launch ". Moor account of his and other fans through experiments and actual firing in the air the SSB system. But the article does not have a lot of interest, until in 1947 a new experiment carried out in the amateur band.
Radio Act of 1927 only lasted for seven years, in 1934 Congress passed the Communications Act. The Bills did not immediately have an impact on radio enthusiasts, but fans from the activities by the FCC restrictions, and continues to this day.
Hiram Percy Maxim, a veteran enthusiast, ARRL and IARU one of the founders, in 1936, Xie. He is set to be a large number of outstanding figures: leaders, writers, photographers, engineers, entrepreneurs, from amateur radio has lost a friend.
DX on the continued high interest, in 1937, discussed a wide range of what is meant by a "country (the country)", ARRL announced plans to DXCC. But what kind of entity to the DXCC award-winning doubt until 63 years later.
In September 1939, war broke out again in Europe. The majority of European countries to stop the activities of amateur radio. The majority of Commonwealth countries also left the amateur radio, including Canada. United fans to continue its activities, although the DX station disappeared from the airwaves, but the west coast of the magazine "Radio" is still in the first year they announced the DX match to be held in 1939.
1940 - War and Peace
1940s enthusiasts in the United States is still very active in the air, but the long-distance communication has become in the past. In 1940, the United States banned the FCC radio enthusiasts in the United States with foreign radio communications. In addition to the U.S. FCC also provides for "outdoor" and "amateur radio emergency organization", the prohibition of mobile stations in the following 56Mhz.
December 7, 1941 attack on Pearl Harbor occurred in the United States, the United States suddenly entered a state of war. Although those who have both technical skills to operate the radio "war emergency radio service" members of the 112M on training, but the United States amateur radio activity or an immediate halt to the activity. As a participant in the "war emergency radio service" is very important and very serious, but as a general lack of the way the fans happy.
At the beginning of the war, about 60,000 Americans have the license. Nearly 25,000 people in the armed forces during World War II to work. The remaining 25,000 people in the important war industry or as teachers in military schools.
The difference is that with the First World War, ARRL during the war and opening up communications business. "QST" continue to adhere to the issue, but because of paper rationing during the war, so the number of pages of the magazine than before. ARRL publication of military and civilian training more, in 1942 the most popular special issue of national defense Handbook (radio manual) was published.
Early in 1945, has indicated the end of the war, some of the New York fans are convinced that the coming of peace, with the end of the war, amateur radio spring just around the corner. They were in January 1945 published a new magazine - "CQ". In the same year in the enemy's defeat on August 17, just four days after the amateur radio enthusiasts in the VHF, to the summer of 1946, from 3.5 to 30 MHz, all of the amateur band are all open.
5 to 2.5 the previous paragraph wave was 6-2 in place of the UHF section. Long-distance short-wave communications have become active, DXCC plans to start all over again. Order on the VHF and UHF love the excitement of the fans as a result of excess military supplies to lower prices significantly.
Of course, short-wave enthusiasts have received a great, over-the letters, mail, high-power tubes, parts and components, almost all eager to get everything from local business center remains to be friendly. The remaining machines is also promoted to the fans, a new model sent a letter RTTY (radio-) way. During the war, some of the fans in the military has used RTTY, the end of the war, the country's excess machines will soon disappear and appear on the fans in the studio.
Legitimate fans were happy to return to the air, the public are also happy to buy television sets, fans and a major threat to interfere with television followed, terrible TVI. TVI problems with the passage of time to gradually reduce, but never completely resolved. Household electrical appliances for household electrical appliances, as well as interference arising from the interference continue to haunt us, but far from depressing 50's TVI as serious.
Also remember that in 1933 the "R / 9" magazine published by the "technical SSB" operation it? Many people tried. In September 1947, Mike Villard, W6QYT lovers and a group of students at Stanford University beginning of the experiment SSB. SSB in the past 10 years, appeared on the band (AM) with bilateral AM words. In addition to a very small number of AM fanatical fans, SSB has finally been replaced. AM fans of these very simple reason is that like the operation of the old equipment as well as the letters AM like the kind of machine excellent voice modulation.
50 era - the normal state
The early 1950s, in 1951, announced that amateur radio license as a result of structural adjustment under attack by amateur radio. FCC announced that amateur radio license from the primary, and the super-class technicians, together with the old A Class, B Class and C categories were replaced by high-level, the general level and a conditional class. The junior Licentiate a one-year, non-renewable, two short-wave band on the part of the enjoyment of the right to the use of CW, both in the UHF band on the part of the paragraph entitled to the use of "words". Level technician who is strong demand in more than 220MHz for VHF and HF experiments, and did not participate in the 13 words per minute of the test established by the fans. The two new licenses through 5 words per minute test. If the number of new fans, the new licensing division was a great success.
In almost less than a year later, in December 1952, FCC license once again change the structure of the set, the registration is no longer a new high-level license, and revoked the special high-level and short-wave license again, "words" on the privileges. The junior-level technicians and licensed the right to remain unchanged, the ultimate level technician was 6 meters and 2 meters in the rights of communication.
In the meantime, a technological revolution took place gradually, people began to use the material known as the transistor, the transistor device on the article also appeared in the amateur radio enthusiast magazine. 20 era as the use of "sparks" of the equipment fans know tube, tube users now have to learn the knowledge of the transistor.
60 era - the incentive licensing system
60's amateur radio community is an exciting era. This decade has brought reflection on face communications, satellite communications and Oscar FM relay communication technology, and the age of 60 will always be unforgettable and exciting rather than technical achievements, but the incentive system for the concession.
Dating back to 1952, FCC abolished the fans in the short-wave on the incentive system of licensing; general level, and high-level special license to give the same rights. Over time, many fans believe that they are among those with high-level license of a lack of communication enthusiasts privilege hinder the development of technology. The results in a few months after the QST magazine and other magazines, tabloids in the club, at the meeting, in the air and so on, there have been debates on the issue, ARRL request of the FCC to restore incentive prerogative of fans. 1963 filing, the request to resume high-level license privileges, the senior class and not the prerogative of the new license, but the proposed lifting of the general license in the 80 meters, 40 meters, 20 meters and 15 meters ", then". Since the 50's and the creation of primary-level technology licensing, the United States to the ranks of radio enthusiasts each year by 10% to 8% growth rate, once the debate began, the growth rate will decline sharply.
Has continued to argue that in 1967, FCC announced his decision: to restore the incentive license privileges. 80 meters, 40 meters, 20 meters, 15 meters and UHF paragraph 6 of the band set aside for low-and high-class license holders, the band from the low level of ordinary fans in the use of withdrawal. Suffice it to say that the majority of ordinary fans are very unhappy level would be sufficient.
In 1967, relaxed the junior level technicians and license rights, the expansion of the short-wave ", then" the band, to amend the senior class and low-band exclusive license details. Having said that, by the FCC in 1967 decided to detail the band's arrangements are still in use. 33 years later, there are still about 60 people during the incentive privileges of the outcome of the debate hatred.
Incentive licensing system is by no means the only major 60s. For example, in July 1960, for the first time in the 1296MHz on the moon through the reflection of two-way communication in the realization of Massachusetts, took place in W1BU and act as the vanguard of W1FZJ, as well as by the W6HB led by California's Eimac Radio Club. Only 1 more than a year after the Amateur Radio Satellite OSCAR to leap into space. This is far from world-famous Silicon Valley region of the crystallization of the wisdom of radio enthusiasts. They plan to launch 3 satellites, and then to the AMSAT-command, Maryland-based Amateur Satellite Organization, the Organization of the United States is still the most important amateur radio satellite research organization. 60s for the first time there have been amateur FM relay, is destined to change the wave 2 can make use of the properties.
In the 1970s - and the communications relay data communications division (Packet radio) times
1970's most impressive is the 10-year FM relay. Not because of the 1970s invented the FM relay, in fact, a long time ago invented the FM relay. But in this decade, amateur FM relay in the VHF and UHF band on take-off and then gradually expanded to 2 meters, 1.25 meters and 70 cm band.
Amateur FM relay of the revolution can be traced back a long time ago. 1939 relay was used in paragraph 5 wave, but in essence said that in experimental fashion, but has never been widely popular. 1950 AM to relay began, distributed nationwide. Since then relay the idea began to pop.
Commercial FM relay system greatly promote the success of the amateur FM relay. After World War II, found that users of commercial FM network to the user's movement in value. In 1950, a large number of manufacturers producing equipment to meet this vision. With the new system of popular channels congestion. In order to reduce congestion, FCC urged them to reduce bandwidth business users, commercial users have to do so, the results of 1960, commercial users of that date, but in fact full of useful devices on the market a lot of excess. The frequency of these facilities close to the amateur band of 6 meters and 2 meters and 70 centimeters, can easily be converted to amateur radio enthusiasts will be able to use the equipment. With the addition of the establishment of an amateur FM relay, a large number of business after the reform, low-cost hand-held and mobile devices increased demand, both domestic and foreign manufacturers. Amateur FM relay into prosperity.
With the relay system throughout the United States, a new quiet revolution in progress. We thank the Canadian Radio-lovers and friends in the early work. Based on the digital revolution, the East has been deeply attracted technology enthusiasts to send. Canada's division of the experimenter data communications technology experiment began in 1978. To 1979, Doug Lockhart, VE7APU has begun to provide packages for fans. Best-selling package quickly in the late 1970s packet data communications have emerged gold rush. ASII Unfortunately, the code is not permitted by FCC rules, so even though the experiment to continue, the United States law does not allow their fans or fans and Canada between this form of communication.
Another major incident took place in Geneva in 1979 of the World Conference on the management of the radio. At the final meeting, after the U.S. delegation to lobby for fans of the three new band, that is, 10MHz, 18MHz and 24MHz.
In the 1980s - and the space division of radio data exchange
In March 1980, FCC finally allowed to use the ASCII code in the United States. This PC with growth in all of a sudden, and set fire to groups of amateur radio enthusiasts to exchange data communications and other data communications fanatical pursuit. In Washington, DC, the amateur radio research and development as the core members of the company represents a group of data communications division of the zealots. AMSAT and their co-operation is responsible for the first time ARRL amateur radio computer network meeting. From out west, and Tucson, Arizona set up a TAPR (Tucson Amateur Packet Radio Data Communication Organization). TAPR organizations in the production of end-node controller, the data communications division for the development of adding fuel to the flames.
In the short-wave digital communications are also booming. In 1982, Peter Martinez, G3PLX, combined with SITOR agreement, the computer will be used for short-wave communications, created AMTOR - the first amateur short-wave digital communications, and to provide automatic error correction method of communication.
In the meantime, the fans were so excited that in 1983, fans Owen Garriott, W5LFL, as the space shuttle into space by astronauts. Garriott has been carrying a 2-meter equipment, from space for nearly 300 of the contact. Since then, each time in space flight include amateur radio enthusiasts. In recent SAREX program (the Space Shuttle Amateur Radio Experiment), Roy Neal, K6EDU to take the lead in the beginning of the world to help students understand the fantastic universe and space program. At the same time, the benefit of the new enthusiasm and new amateur radio enthusiasts.
In a point of order, in 1984 embarked on a very successful test of the obligations of a co-ordinated program. In addition, FCC issued PRB-1 Act, providing for the protection of radio enthusiasts.
Last but not least, in July of 1989, in line ARRL voted in favor of the FCC's request to set up more than 30MHz without the need for Morse code skills of the license exam. Many people believe that no code of the times up.
In the 1990s - no need to code and licenses digital communications revolution
Despite the holding of the junior technician class license and the lovers of Morse code speed requirement of only 5 per minute code, but Morse code is still a lot of potential obstruction of amateur radio enthusiasts. They may point out that throughout the world in military and commercial communications in Morse code is to reduce the role. Followed by amateur radio community in the heated debate ARRL to make a new proposal to set up more than 30MHz without a required code technician class license. 1991, the FCC agreed to this proposal, once again active in amateur radio activities. In the late 1990s, the United States licensed amateur radio enthusiasts of 700, 000. However, it was predicted that the amateur radio to bad luck. "School code," was born in the air, the establishment of transit, to join the club and emergency rescue organizations, to establish leadership.
Then it appeared on the Internet, in a short span of a few years dramatically changed the world. In the early 1990s, Bo and scholars have predicted that we will enter a new era of communication revolution.
When we are about to leave the 1990s, Bo scholars of early predictions have been confirmed. Who can believe that only a few years, the United States of phone calls per minute to only 5 cents, while the British call the phone only twice the price? Who can believe that the emergence of the World Wide Web has changed the business almost a century or more of the model? These are all amateur radio activity on the challenge. Computer and the Internet charm of countless young people who used to work in radio activities were technically very easy to master. These lead to such a prediction: towards the end of amateur radio, replaced by a computer on the Internet in particular. Fans seem to accept this fact. Today, the majority of the members of the ARRL use of the Internet. DXer the use of packet-based network and configure the network, automatic position reporting system (APRS) use the Internet for distance transmission. Space enthusiasts have been tightly surrounded by computer, using the Internet to exchange information and software, such as Ebay fans in the sale of surplus network equipment, information on group discussions.
PSK31 exciting short-wave digital communications in the way of useful software for free access to the network, so that helped. Expedition enthusiasts in contact after a short period of time, even in remote places, you can publish Web LOG (Radio Diaries). This, of course, would like to thank the Amateur Satellite PACTOR, as well as COLBER and short-wave digital communications technology.
Computer also amateur radio communications into a new world of experiments, for example, computer and radio link can be made many years ago can not imagine the number of experimental communications technology. TAPR is a positive outcome of the efforts, for example, will eventually provide the spread of the electromagnetic spectrum, and other devices. It is clear that the Internet for amateur radio "threat" is a bit exaggerated. On the other hand, computers and the Internet to make amateur radio more substantial and more interesting, more attractive than before.
In the 20th century to a close, ARRL and the FCC have once again put the United States to change amateur radio enthusiasts of the license structure. ARRL in the most controversial proposal is to reduce the content of the short-wave license examination of the Morse code speed requirement. At time of writing this article, FCC has responded to the ARRL suggested that many do not see the contents of opposing views. If this proposal were implemented, then the U.S. Amateur radio will be moving towards a new road, but this is not a bumpy road, there is a forward slope of the road, but it is not a downhill path.
He used to be one of those, in particular, Faraday, Maxwell had a great impact on the work, but many of the same generation MAxwell convinced that his new theory is correct. It will not rock-solid than the smaller experiments to those who break the wall of suspicion. German physicist H. Hertz is not just these, in 1880, he was not in accordance with the Maxwell equation predicted the occurrence of electromagnetic waves, detection and measurement of the properties in a series of famous experiments. Hertz, though, in addition to their intellectual challenges beyond those found in the waves, there is no specific interest, but he eventually found that the radio was used in human development. In the race to continue.
One of the participants in the race to develop a radio that the young Italian G. Marconi. He is a physics and electrical science is very interested in boys. He's learning at school and was a major subject is likely to become famous in the electromagnetic wave communication, in 1894, he started this project seriously. England in 2002 after he made a radio device can be used. In a performance, Marconi British officials in the presence of the face, had more than 2 miles away from radio communications. This was a Surprisingly, the great exploits, and has since launched Marconi's career. Later, as the old saw blade and Latin America, is history.
Who was the first amateur radio operators? We may not know. Some people say that Marconi. Marconi life permeated with the enthusiasm of amateur radio, and in the mind to consider himself as a amateur. Nevertheless, he chose to dedicate his life to the radio communications market; he did not like the family as an amateur radio license acquisition and operation.
I said before, and we may not be able to identify who carried out the first amateur radio operators, but the British L. Miller was indeed the honor of strong competitors.
L. Miller in the history of amateur radio has a strong position because he is the first publication of his brief amateur radio equipment in writing and mail. In his article published in January 1898 in London to issue a "model of electrical engineers and amateur." His readers to keep in mind this article. March 1898 publication of "EA" wrote that he has a 2-inch spark coil and three brass balls, but no structural details. (Which of the three brass balls is considered by the Miller announced by the three devices one of the letters.) Followed by some Americans, in the July 1899 Journal of the American electrician on the subject published Less than 3 letters. The explosion of interest in the back of the decade, but in the 19th century to shorten the amateur radio and our distance.
The first decade of the twentieth century: the beginning
As of the beginning of the 20th century, the rapid development of the business. 1901, Marconi and the use of high-power antenna to realize the huge trans-Atlantic radio communications. Amateurs use their advanced equipment to continue to improve and experiment, in June 1902 Boston Magazine's "amateur" has published in its detailed structure of the article. From there, it is clear that many of the skills at that time had been found until today, amateurs are still using: If the article said, the balance feeder.
These early transmitters capacitive full use of the discharge gap oscillation generated sparks. These early spark transmitter is capable of producing radio frequency, but is the natural frequency bandwidth, make it difficult, and the two neighbors can not normally be in writing at the same time. Receiver is a simple detector, usually metal detector powder, the subsequent emergence of a more sensitive detector of ore.
At that time, of course, not rules, the amateur call sign to identify their own, often using the acronym for the name of the operator.
In 1904, when the British JA Fleming invented the first vacuum diode, "Fleming vacuum tube", a hint of the future development opportunities have emerged. In 1906, L. Fleming Defusite in an increase in the vacuum tube grid network, made its first three-tube, named the "Audion" transistor detectors are very effective, but most of the hobby Who are too expensive. After a few years until it was used for radio frequency occurred. At the same time, ore and spark transmitter receiver channels have also been provided for.
10 years on behalf of the twentieth century - the rules
In early 1900, amateur radio transmitter initially be limited to the scope of the yard, and then to the development of the block. With the increased power and technological progress, by 1912 well-designed 1,000-watt (spark) the launch of radio range to reach almost 100 miles. Those who have more power stations could be the work of hundreds of miles. High-power usually means more interference, so the rules of the establishment of more and more strong voice.
In fact, from the Congress in 1910 began to investigate the radio. In 1912, after more than a dozen different motion on the assessment, Congress finally passed the bill radio. So that radio enthusiasts have been recognized for the first time. At the same time, the bill has a little at first to die in the amateur radio: fans can only be restricted in the work of the UHF section 200. During that period is generally long wave that can improve long-distance communications. The 200-long wave of "short-wave" is considered useless, and some people even expect radio enthusiasts have crowded in this useless band and eventually turned to love to give up the pursuit of other radio-loving.
But the plot did not succeed, although the radio in 1921 after the implementation of the Bill of decline in the number of fans, but soon the United States amateur radio began to gradually grow, in 1917, the radio enthusiasts in the air more than 6,000 people.
Many fans of other enthusiasts each other through the relay broadcast of the effective extension of the scope of communication. In the United States, the capital of Hartford, Conn., the call sign 1WH, after 1AW for the Hiram Percy Maxim fans realize that if the radio relay broadcast organizations, the news could be more reliable to carry out long-distance transmission. In 1914, the League of American radio was born, and then in 1915 began issuing QST magazine. Today, the call sign "1WH" and "1AW" seems a bit odd, but very early in the ordinary amateur radio. Department of Commerce in 1913 for the fans call sign letters of the rule-making, but there is no need for the definition and prefix. 20, until the mid-and late prefix only.
At about the same time, a radio receiver technology available miracle. 1913 New York amateur radio enthusiasts Edwin H. Armstrong invented the use of renewable accept the work of the tube, to 1915, knowledge of this technology has been widely popular. The new receiver at that time than the higher sensitivity of the detector crystal. Although the tube when the price is very expensive, and many fans Armstrong started the design of the experiment.
1914 First World War broke out in Europe. To 1917, the United States involved, all amateur radio enthusiasts to stop the activities. In fact, amateur radio enthusiasts who formed by Hiram Percy Maxim backbone for the training of radio operators at the time of the Commonwealth of the most eye-catching, and served about 4,000 fans, the ultimate service to the country. The word "service" is very important here, it stressed that amateur radio is an important role - for the public and national service.
The end of war in November 11, 1918 ended after a trial of strength, the United States Navy took control of the radio. With the military service to the fans, they look forward to the abolition of the Navy in 1917 to close the amateur radio command, but failed. Navy fans refused to return to the sky. U.S. amateur radio's future once again uncertain.
It seems that the Navy is determined to continue to control all radio services, even in times of peace, amateur radio On the surface, they do not allow the radio service on the list. To support the Navy's point of view and even to be written into the legislation. U.S. Amateur Radio Union and other opponents of the practice of struggle against the Congress and called for all the fans and their families to their members to write protest. Political pressure did not affect the vote on the legislation, but the Navy refused to allow amateur radio enthusiasts to return to the sky. Finally, Massachusetts on behalf of the William S. Greene heard the voice and vote on behalf of the House, directed the Navy to the end of the ban on fans. Navy to obey the order was to break the deadlock, the United States amateur radio in November 1919 to start activities. This episode was used as thousands of fans to the power of collective problem-solving model has been written into textbooks.
Our other product:
