"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 N279, June 29, 2014
Longwave Radio Broadcasting Stations on High Power
Back at the beginning of the wireless era, it was considered that the most successful procedure to obtain long distance coverage was to transmit with high power on a longwave channel. This concept was true for Morse Code communication back in the 1900s, and the very first plan for worldwide communication was a cascading network of high powered longwave transmitters installed at suitable geographic locations over the intervening distances.
This concept was true also back when radio program broadcasting was implemented experimentally in Europe and in North Africa soon after the end of World War 1. In order to gain the maximum coverage area, and thus the maximum number of potential listeners, the intended goal was to transmit with as much power as possible on a low frequency longwave channel. Back then of course, what was considered to be high power was in reality quite low as compared to longwave broadcasting stations these days.
In 1924, for example, the English radio magazine Modern Wireless listed twenty longwave stations on the air in nine different European countries, though only three are shown with a power of 10 kW or more. It is probable that the power rating given back then was for the level of power into the transmitter equipment, rather than the output power from the transmitter to the antenna system, almost a 50% loss. These three higher powered stations were:
As time went by, the level of power for the highest powered longwave broadcasting stations in Europe began to increase. Four years later in 1928, another station listing shows the three longwave broadcasting stations in Europe with the highest power level, and these were:
Four years later again in 1932, Radio Luxembourg was launched with 150 kW on 1250 metres, 240 kHz and it was touted as the highest powered longwave broadcasting station in the world. An English language service was introduced in 1933 and the frequency was changed several times before settling on 230 kHz.
It was during the 1930s that strange intermodulated programming was first noted in the reception of radio transmissions from Radio Luxembourg with 150 kW on 230 kHz. The programming from a longwave transmitter in Switzerland could be heard mixed in with the programming from Radio Luxembourg even though the two stations were transmitting on different channels.
Radio Monitors at Eindhoven in Holland observed this strange phenomenon as did listeners in Gorky in Russia who heard the programming from Radio Moscow mixed with Radio Luxembourg.
Over a period of four years, two physicists, Australian V. Bailey and Russian D. Martyn, studied the phenomenon now known as the Luxembourg Effect, and they discovered that two very strong longwave signals can cross modulate in the ionosphere, even though the signals are on different low frequency wavelengths. No more than 10% of the signal from the lesser station will cross modulate into the signal from the stronger station and the two stations have to be on the same great circle path as the listener in order for the effect to be heard.
Apparently an attempt by the BBC in 1932 to upgrade station 5SX at Swansea on the south coast of Wales to a power level of the listed 158 kW on 1411 metres, 212 kHz, did not come to fruition.
However, at this stage, it is apparent that a power race in Europe had begun in earnest. In 1933, Russia was listed with six longwave broadcasting stations at 100 kW and above, including the Moscow station RV1 on 1481 metres, 202 kHz with no less than 500 kW. Warsaw Poland was also listed at 120 kW, on 1411 metres, 212 kHz.
By the beginning of World War 2 in 1939, half a dozen more European countries had longwave broadcasting stations at superpower level, and these were:
In 1962, Luxembourg increased the power of its longwave transmitter then on 233 kHz to 600 kW to counter interference from Russia. In 1972, the longwave transmitter at Junglinster in Luxembourg was replaced by a 1400 kW unit at a new location, Beidweiler; and in turn this facility was upgraded two years later again to a massive 2000 kW, that is, two megawatt, on 236 kHz, later adjusted to 234 kHz or 1282 metres under the Geneva Plan of 1975.
There was a time when Iceland majored in the installation of longwave radio broadcasting stations due to the fact that their island is located so far north, and rather close to Europe. During the long winters with short daylight hours, many mediumwave stations in Europe propagate strong signals into Iceland, often interfering with the programming from any mediumwave stations located on the island. Hence for a long period of time, Iceland has emphasized the value of longwave radio for local and island wide coverage.
These days, though, with the availability of FM radio, Iceland has moved into that section of the radio spectrum, though they have still retained two longwave stations:
In the current 2014 WRTVHB, 29 longwave broadcasting stations are listed in 16 different countries in Europe, North Africa and Iceland. The listed power for these stations ranges from 50 kW, up to 2 megawatt, the latter being used at three different locations:
Due to the sophisticated electronic equipment in use these days, you will hear audio quality from most of these modern longwave stations that is absolutely superb, even though the transmission frequency is quite low. However, one of the main problems with longwave transmissions is that there are only 16 channels in the entire band, which runs from 153 up to 279 kHz.
Notwithstanding that, high powered longwave broadcasting is still a viable means today for reaching listeners in Europe, Russia, North Africa and Iceland, especially where large areas of territory need to be covered.