SHORTWAVE RADIO HISTORY
Most of the activity of radio amateurs is on the shortwave bands and it is mainly used by those who are active in DX contacts. Radio amateurs played a very important role in the history of short waves radio communication.
The frequencies that have been used at the beginning of the wireless telegraph era (from 1900 and on) were between 50 KHz and 1,500 KHz (long and medium waves). All the services (Land, Maritime, Aviation, Experimental and Amateur) operated on this frequency spectrum without organized segments division. The wireless telegraph services have been based on Morse code transmission, with very high power Spark-Gap transmitters and very large and long wire antennas.
In 1912 the long and medium bands were divided into dedicated segments for land, maritime and aviation services. To avoid the interference from the experimental and amateur stations, they have been allocated in a higher band of 1,500 KHz to 2,000 KHz. In those days the frequencies higher than 2,000 KHz, were considered as impractical and not suitable for long range radio communication. As the propagation of long and medium waves is based on ground waves, the experience showed that in higher frequencies the reception level is decreased. In addition, there was a difficulty in building spark-gap transmitters at higher frequencies. When the Triode vacuum tubes have been used in transmission and reception circuits, there was a problem in operating at higher frequencies due to the capacitance between the Grid and Anode. This problem was solved later on, by adding the Neutralization Circuit and the development of the Tetrode Vacuum tube.
Radio amateurs around the world operated at the Band of 1,500-2,000 KHz with very small transmitting power, comparing to the public and commercial wireless telegraph services. They designed and built antennas and resonance circuitry for the higher frequencies, achieving radio communication to distances of thousands of kilometers. In 1922 radio amateurs in Europe received transmissions from North American radio amateurs and European amateurs have been received in the USA, but no two-way communication was performed. The first two-way radio communication between amateurs in the USA and Hawai was at the end of 1922.
There was a need for extending the amateur radio band to much higher frequencies, due to the congestion at 2,000 Khz. Only several amateurs received a special permission for experimental operation at frequencies higher than 2,000 KHz. The experiments on 3 MHz, resulted vety much longer distances. The first two-way Trans Atlantic communication between radio amateurs was in 1923 between 1MO station in the USA and G2KF (J.A. Partrigge) in England.
1MO Station Transmitter G2KF Amateur Radio Station
In 1924 two-way Trans Atlantic contacts have been conducted between many radio amateurs. In September 1924 amateurs in California contacted amateurs in New-Zealand. In October 1924 English amateurs performed the longest distance communication lasting 90 minutes, with amateurs in New-Zealand.
In October 1924, the Third Radio Convention in the USA allocated to the radio amateurs the new frequency bands 80, 40 and 20 meters (3.5, 7 and 14 MHz). These allocations have been adopted around the world. The 1927 International Radio-Telegraph Convention in Washington, allocated the 10 meters (28 MHz) band. The 15 meters (21 MHz) band was allocated to amateurs in the USA in 1953.
Guglielmo Marconi the wireless pioneer was active in experiments with wireless telegraph since 1895. His company in England was the main contributor to the development and application of wireless telegraph around the world. Marconi was very interested in the achievements of radio amateurs in the shortwave band. In 1923, He asked his assistant Charles Franklin to conduct a wide range research on the characteristics of short waves propagation. Marconi requested to examin the ability to conduct stable and reliable long distance communication during day and night and at all the seasons.
Charles Franklin operated a 25 Kilowatt transmitter on 3 MHz with a very large antenna in Poldhu, England. In July 1923 at night a radio contact was conducted with the yacht of Marconi at the Capo Verde Island (West Africa). In September 1924 there was another radio contact with the yacht of Marconi at the Beirut Port (Lebanon) on 11 MHz during day and night. Franklin continued the improvements of the short wave antennas and developed the high gain Directional Curtain Antenna.
Marconi was very encouraged by the achievements of Charles Franklin and in July 1924 he started the negotiations with the British Postmaster General about the contract to establish a network of shortwave wireless telegraph stationss covering England, South Africa, India, Australia, and North America. This network was the skeleton of the “Imperial Wireless Network” that started to operate in 1926-7.
Shortwave Propagation Theory
At the beginning of the 1900’s, the scientists had no reasonable explanation about propagation of medium waves to distances much longer than the horizon at night. There was no approved scientific explanation to the very long radio communication ranges that have been achieved at the short wave bands and the “Dead Area” between stations. Two different scientists, the American Arthur Kennelly and the British Oliver Heaviside came out in 1902 with the theory that around the globe there is a conductive layer that reflects the radio waves back to earth.
Charles Franklin Oliver Heaviside Arthur Kennelly Edward Appelton
The theory of Heaviside and Kennelly was not accepted by the scientists at that time, because it did not comply with the conditions for reflecting light waves. This theory was finally approved by the British scientist Edward Appelton. He researched the ionosphere layers and approved that they cause the sky waves to be reflected and to enable the propagation of short waves around the world. Edward Appelton was awarded with the Nobel Prize in physics for this research 1n 1947.
In 1928 about half of the international telegrams were delivered by short wave radio and the other half by submarine cables and long wave radio systems. This process continued until the domination of the short wave communication brought to the end of long wave radio communication. The submarine cable systems continued to operate, but in the 1960’s the first communication satellite TELSTAR started to operate. The share of space communication continued to increase gradually by pushing out the international short wave communication systems. At the beginning of 21st century the use of shortwave for international radio communication dropped drastically.
Shortwave listeners and radio amateurs oldtimers, are noticing the tremendous difference between the spectrum-scanning during the mid 20th century, comparing to our days. The spectrum was congested with Morse code, voice, teletypes, radio-telephone, facsimile and more types of radio communication. These activities do not exist more and the remained activity is of international radio broadcasting stations, civil and military H.F. SSB radio communication. Radio amateurs, the pioneers of short wave radio, are still the main users of shortwave radio communication on Morse code, SSB and digital modes.
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