"Wavescan" is a weekly program for long distance radio hobbyists produced by Dr. Adrian M. Peterson, Coordinator of International Relations for Adventist World Radio. AWR carries the program over many of its stations (including shortwave). Adrian Peterson is a highly regarded DXer and radio historian, and often includes features on radio history in his program. We are reproducing those features below, with Dr. Peterson's permission and assistance.
Wavescan N284, August 3, 2014
A Blast from the Past: Mediumwave Broadcasting Stations on High Power
A few weeks back here in Wavescan, we presented the story of radio broadcasting with high power on the longwave band. On this occasion today, we present another similar story, regarding radio broadcasting with high power on the mediumwave band, under the title: A Blast from the Past. So let's go way back to the introductory events, in the year 1925.
Back at that time, the power output of licensed mediumwave radio broadcasting stations throughout the world was quite low. Many stations were on the air with a power output of just 5 or 10 watts, and occasionally lower; and even then just 100 watts was a common power level.
A comparison of entries in various radio lists at that time, reveals that the highest power level in 1925 was just 5 kW, and we should remember that the rating for transmitter power was calculated as the input to the transmitter itself, which would be approximately twice the calculated power output to the antenna system. Thus a 5 kW listing in 1925 could be interpreted as approximately 2.5 kW output into the antenna system.
In 1925, the radio lists show that 5 kW was the highest power rating for a mediumwave station anywhere in the world. There were just eight stations listed at 5 kW in the United States, four in Australia, and just one in Canada, making a world total of only thirteen stations on the air at this transmission level.
Even then, the lone Canadian station was in the planning stages and not actually active on the air. This station was CKCW and it was granted a construction permit for a location near the city of Toronto.
However, station CKCW was never erected as originally intended near Toronto, but instead the license location was transferred to nearby Bowmanville under an adjusted callsign CKGW. This new station CKGW was subsequently inaugurated some three years later in 1928 and it became well known due to the fact that an associated low power shortwave transmitter carried a relay of the mediumwave programming under the callsign VE9GW.
The original call CKCW was eventually assigned to another station in Moncton, New Brunswick which went on the air in 1934 with a more normal power of 100 watts on 1370 kHz.
Interestingly, in that same year 1925, the American radio magazine Radio Broadcast for January printed a prophetic item on page 474, forecasting an increase in power for mediumwave stations. The writer conjectured that one day we would listen to super power mediumwave transmitters with a power even as high as 10 kW!
During the following year 1926, a higher power level began to appear in the mediumwave station lists, with two American stations at 10 kW (KGA Spokane & KJR Seattle), another at 20 kW (WOK Chicago), and one at 50 kW (WJZ New York).
During the 1930s, the mediumwave power race was on throughout the world, with a maximum power rapidly increasing up around 100 kW. Additionally, many stations in Europe and Asia were operating at a level around 50 kW.
In 1933 for example, the highest powered mediumwave station was listed as station OKP near Prague in Czechoslovakia with 120 kW on 614 kHz. Radio Moscow in Russia sported 100 kW on 704 kHz, and XGOA in Nanking, China was shown with 75 kW on 680 kHz.
During that same era, six stations in France, Germany and Switzerland are listed with 60 kW; and eight stations in Sweden, England, Scotland and Italy are listed with 50 kW, including the famous 2LO in London.
During the mid and late 1930s, the power race was demonstrated further afield, with both Vienna on 592 kHz and MTCY at Hsingking in Manchukuo at 100 kW; in Japan, JOAK2 in Tokyo operated at 175 kW on 870 kHz. The highest powered mediumwave radio broadcasting station in the South Pacific was the well known national station 2YA in Wellington with 60 kW on 570 kHz. In those days, 2YA was often heard in the United States, as well as right across Australia.
During the early 1940s, more than fifty mediumwave stations in the United States were on the air at a power rating of 50 kW, which by then was the highest that the FCC would permit for regular broadcasting. Most of these high powered American stations were operating on a Clear Channel, with little or no co-channel interference.
After World War 2, the power levels on mediumwave continued to grow, until now half a century later, there is a multitude of mediumwave transmitters on the air with a rated power of one and two megawatts. For the transmission of superpower radio energy, usually two or more transmitters are coupled, sometimes into separate antenna systems on the same frequency, and sometimes with a combined power output into the one antenna system.
For example, Saudi Arabia is on the air with mediumwave transmitters listed at 2 MW, that is 2,000,000 watts output. These super power two megawatt broadcasting systems in Saudi Arabia are heard on 594, 648 and 1521 kHz. Hungary is also listed with 2 MW on 540 kHz, and Vietnam on 1242 kHz. Both North Korea and South Korea radiate 1.5 MW on 657 and 972 kHz. Both Russia and China are on the air with 1.2 MW via a total of six mediumwave channels.
At 1 MW, that is with one million watts, at least 30 mediumwave stations are on the air in Europe, the Middle East, North Africa and Asia. The countries in Asia with such high-power are India, Pakistan, Taiwan, Siberia, Bangladesh, China, Thailand and North Korea. In addition, the Voice of America is on the air with 1 million watts on 1575 kHz in Thailand, and 1170 kHz at Poro in the Philippines.
On a coming occasion here in Wavescan, we plan to present the story of superpower mediumwave stations in North America.