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TABLE OF CONTENTS
A Short History of the Marconi Trans-Atlantic Receiving Station in Louisbourg
Figures 1 to 22: The Original Station, 1913-1914
Figures 23 to 32: During and After World War 1
Figures 33 to 36: Louisbourg Station Site Today
A Short History of the Marconi Trans-Atlantic Receiving Station in Louisbourg
The construction of a receiving station in Louisbourg, Nova Scotia and a similar one in Letterfrack, Ireland in 1912-1913 represented the final phase of the establishment of the first transAtlantic radio communications service. This service was the first link in the worldwide radio communications network that we take for granted today. The principal events leading up to this were the following.
1895 - Marconi transmitted radio signals over a distance of more than a mile at his home near Bologna, Italy, demonstrating the potential of radio as a means of long distance wireless communication. This event is being celebrated in 1995 as the one hundredth anniversary of the invention of radio.
1897 - The Wireless Telegraph and Signal Company was formed in London, England, to exploit Marconi's invention commercially. Initially the marine industry was its main customer.
1901 - On December 12 Marconi received the first trans-Atlantic radio signals at St. John's, Newfoundland. These signals were transmitted from his powerful station in Cornwall, England.
1902 - On December 15 Marconi transmitted the first official trans-Atlantic wireless telegraph messages to Cornwall from his new station at Table Head in Glace Bay, Nova Scotia. The Marconi National Historic Site is located at the site of this station.
1907 - On October 15 the first trans-Atlantic wireless telegraphy (radio) service was opened to the public with the exchange of official messages between new stations at Marconi Towers, near Glace Bay, Nova Scotia, and at Clifden, Ireland.
The trans-Atlantic stations took turns transmitting messages because a station could not operate its receiving equipment while its transmitter was operating. When business justified it, Marconi removed this limitation by building dedicated receiving stations, in both Cape Breton and Ireland, that were far enough from the transmitters to avoid interference from them. This allowed the receivers to operate continuously, and messages to be transmitted both ways across the ocean simultaneously. Such a simultaneous twoway service is called a "duplex service". The new receiving stations were at Louisbourg, Nova Scotia, and Letterfrack, Ireland, and the duplex trans-Atlantic service began in 1913. The following is a short history of the Louisbourg station.
The Louisbourg Station
It might surprise radio listeners who associate long distance communications with "short wave" to know that the first trans-Atlantic service operated at very long wavelengths or low frequencies. Marconi Towers transmitted to Letterfrack at a wavelength of 8000 metres (37.5 kHz), and Clifden transmitted to Louisbourg at 5500 metres (54.5 kHz) [note 1]. There were several reasons for using wavelengths in this range. At long wavelengths, multiple reflections between the ionosphere and the earth provide a steady signal at long distances both by day and night. Even longer wavelengths (VLF band) also provide a steady signal, but the large size of the antennas required for efficient transmission make them impractical for commercial communications. At shorter wavelengths (MF and high LF bands) the ranges are smaller, especially in daylight hours, and the transmitting equipment of the day was less efficient. Hence Marconi's choice of wavelengths for the trans-Atlantic service was about optimum, considering the state of the art of radio at that time.
It might also surprise radio engineers today to realize that a reliable trans-Atlantic service was achieved without the aid of electronic amplifying devices such as the vacuum tube and transistor. The Marconi transmitters at Table head and Marconi Towers generated radio frequency signals with the aid of a high voltage electric spark, following the example of the original radio experiments of Heinrich Hertz. The spark created a short electrical impulse that produced the necessary radio frequency currents in the antenna. The early spark transmitters were either untuned or broadly tuned, and interfered with one another considerably. By 1907, when the trans-Atlantic service began, tuning (called "syntony" in the early days) was much improved, as the assigned frequencies and wavelengths of the trans-Atlantic stations suggest. In spite of crude technology, the power and efficiency of the transmitters (at least up to the antenna) were not far behind their modem counterparts.
On the other hand, the radio receivers in 1913 were millions of times less sensitive than modem receivers because they lacked vacuum tubes or transistors to amplify the signals. The Louisbourg receiver consisted basically of an antenna employing an aerial wire and a ground connection (transmitting antennas were similar), tuning circuits, a detector and a recorder.
The detector converted the incoming radio frequency signals into direct current pulses capable of operating a recorder. Many weird and wonderful devices were used as detectors in the early days of radio with varying degrees of success, including the coherer, frogs' legs, brains [note 2], the magnetic detector ("Maggie"), the electrolytic detector, the crystal detector (a diode consisting of a pointed metal wire in contact with one of various minerals), and the vacuum diode (Fleming valve), to name a few. Some of the more bizarre forms of detector were tried simply because the principle of the first successful detector, the coherer, was not fully understood, so experimenters were willing to try their luck at just about anything. The rectifying action (conversion of alternating current to direct current) of the crystal detector and the Fleming valve was understood, and these detectors became quite popular.
The first Louisbourg detector was the carborundum detector, a rugged crystal detector invented by General H.C. Dunwoody of the U.S. Army. Marconi used a circuit called the "balanced detector", in which two carborundurn diodes were connected and electrically biassed in such a way that strong impulses produced by lightning discharges would tend to cancel out, whereas the weaker signal that the operator was trying to copy would be detected.
The detected electrical signal either went directly to the headphones of an operator or was recorded. Using a system developed by the Canadian Marconi Company, the high speed incoming messages at Louisbourg were recorded on wax Dictaphone style cylinders that were later played back at a slower speed by the operators for decoding and typing.
A similar process was used in reverse for transmission. Instead of an operator transmitting a message using the relatively slow telegraph key, the message was hand punched on paper tape. The tape was then played on a machine that converted it into a Morse code transmission at high speed. The combination of these transmission and reception techniques permitted radio messages to traverse the ocean at up to eighty words per minute.
From a modem perspective, it is amazing that a reliable trans-Atlantic radio service was established without benefit of electronic amplification. The output of the detector was limited to the signal power collected by the receiving antenna, hence the antenna had to be very large. The main receiving aerial wire at Louisbourg was about one kilometer long and was supported by six tubular steel towers that were about 330 feet (100 metres) high. It was oriented in a roughly east-west direction, with the away from the source of the signal, as was the practice in the construction of Marconi "inverted U antennas. (For some reason, it was not aligned with a great circle bearing joining Louisbourg and Clifden, but was orientated about 18* to the eastward. By contrast, the transmitting and receiving antennas of that period at Marconi Towers were aligned precisely on great circle bearings.)
Although the receiver at Louisbourg and the transmitter at Marconi Towers were tuned to different frequencies (54.5 kHz and 37.5 kHz, respectively), a "balancing-out aerial" was utilized at Louisbourg to further reduce the interference from the Marconi Towers transmitter. This was a long low aerial wire aligned in the direction of Marconi Towers, and roughly perpendicular to the direction of the overseas transmitter. The signal from Marconi Towers received on this aerial was used to cancel out the interfering signal from Marconi Towers that was received on the main aerial.
Although the receiving system in 1913 had no means of amplifying the received signal electronically, the volume of the signal was boosted by an ingenious electromechanical audio amplifier called a "telephone relay". The model used at Louisbourg was the Brown relay. It worked on the principle of an earphone feeding into a carbon microphone, the two sharing a common diaphragm. Several of these Brown relays could be operated in cascade, producing a volume that was high enough for the signal from overseas to be heard with the operator's headphones resting on the table.
The station was located close to the Atlantic coast about four kilometres south-west of downtown Louisbourg, and about one and one-half kilometres west of the fortress. The station buildings were on both sides of a 250 metre long driveway that began at the shoreline road between Louisbourg and Kennington Cove. The station was surrounded by a fence with a main gate at the entrance of the driveway. Proceeding up the driveway, the principle buildings were: on the right, a stable; on the left, a large staff residence called "the hotel"; behind it, the "receiver house", which was the main operations building of the station, on the right, two duplex staff residences, and at the end of the main driveway, a workshop on the right and the manager's (Superintendent of Traffic) residence on the left. This layout remained the same throughout the life of the station. Continuing beyond the driveway in about the same direction (roughly WSW) into the woods was the one kilometer-long line of towers that supported the main receiving aerial.
The aerial towers dominated the landscape and informed the viewer that this was a aerial wire extending westward, major radio station. On the other hand, the buildings were not imposing by comparison with a transmitting station like Marconi Towers. The reason was that the receiving apparatus, which was rather casually wired together and laid out on benches, required little or no electric power, whereas a major transmitting station of the period contained large, high powered machinery, and had its own electric power house to run it.
The largest building was the three story "hotel", which had such amenities as a tennis court on the front lawn and a billiard room. The main operations building, the "receiver house", was a simple, one story structure about 24 metres long. Among the rooms in this building in 1913 were the room containing the receiving apparatus, which was maintained by engineers, a room in which the wireless operator received and recorded messages on Dictaphone style recorders, the landlines room in which several telegraph operators sent and received messages via landlines to both Marconi Towers and local telegraph companies, a room containing a gasoline motor and generator, and an office. This was a twenty-four hour operation, and there were three shifts a day of engineers, wireless operators, and landline operators [note 3].
The efficiency of the duplex trans-Atlantic service was greatly enhanced by land lines connecting the Louisbourg receiving station to North American telegraph systems and to the Marconi Towers transmitter. The former allowed messages to be relayed between the land based telegraph networks and the trans-Atlantic radio link, and the latter allowed the Marconi Towers transmitter to be remotely operated (keyed) at Louisbourg. Thus the Louisbourg station became the communications center of the western terminus of the transAtlantic radio service.
During World War 1 (1914-18), the station was considered to be an important military target, and was guarded by the 94th Highlanders. Presumably the authorities feared sabotage or a commando attack from the sea. The staff of twenty-five now included censors. An album of photographs of the station contains the note that the censor ordered the negatives to be destroyed.
World War I also spurred improvements in the triode vacuum tube (valve), invented by Lee Deforest in 1906. The tube (valve) was developed into the reliable and practical electronic amplifying device that would revolutionize radio and usher in the age of electronics. During the war., vacuum tubes were introduced into Louisbourg receiving circuits, but cautiously at first, keeping the older crystal detectors and Brown available as back-ups at the flip of a switch. In 1916, electric typewriter punches replaced the hand punch to produce perforated paper tapes. The tapes were fed into "Whetstone transmitters" which converted them into Morse code that was automatically sent out by the Marconi Towers transmitter [note 4]. The receiver house was renovated and modified structurally to reflect these new arrangements.
The era of the spark transmitter was now coming to an end. This mode of radio transmission was often referred to as "damped wave", on account of the train of radio waves of decaying amplitude produced by each spark. It was being replaced by Itcontinuous; wave", a system that generated a radio wave of constant amplitude, which was switched on and off to produce the dots and dashes of Morse code. Continuous wave, or "CW", was generated by arcs and by high speed alternators, and now increasingly by triode vacuum tubes as higher powered tubes were developed. CW was rapidly gaining favour because it could be tuned more accurately and it could be modulated to carry the human voice. Also, the vacuum tube CW transmitter could work at higher frequencies, and was simpler to operate and maintain than large spark transmitters with their associated electrical machinery, or arcs with their big magnets.
Unlike the spark, CW required special receiver circuits or apparatus to render a Morse code signal audible. One such arrangement was the "tikker", which chopped the incoming CW signal at an audio frequency rate. This system was used at Louisbourg in a successful experiment in 1915 to receive CW signals from the U.S. naval radio station in Arlington, Virginia [note 5]. In 1915 the Arlington station also made the first trans-Atlantic transmission of the human voice, using a transmitter with over three hundred vacuum tubes. By 1919, vacuum tube technology had advanced to the point where the Marconi company was able to make the first east-to-west trans-Atlantic voice transmission with only three high powered vacuum tubes in the transmitter [note 6]. The transmitter was at Ballybunion, Ireland, and the signal was received at Louisbourg. Vacuum tube technology continued its advance at Louisbourg, first in units that replaced parts of the old receiving system, and after World War 1, as complete rack-mounted receivers with old-fashioned hom style loud speakers, that would at least be recognizable to modem radio operators as radio receivers.
The trans-Atlantic voice transmission ("radio telephony") from Ballybunion to Louisbourg in 1919 had still used a long wavelength (3800 metres, 79.9 MHz), but all that was soon to change. Up to this time, Marconi and others had gravitated toward long relays wavelengths for long distance communications for reasons explained earlier. However, improvements made in vacuum tubes and associated circuitry during World War I allowed tubes to operate at much higher frequencies. Both amateur and professional radio operators began to notice that long ranges sometimes were obtainable at the higher frequencies and shorter wavelengths (HF band) that became known as "short wave". Marconi systematically investigated these wavelengths using transmitters at Cornwall, England and a receiver on board a ship, initially on his yacht Elettra. The surprisingly long ranges obtainable with relatively low transmitter powers convinced Marconi to alter his plans for a long wavelength network of stations that would span the British Empire, and build a short wave network instead [note 7]. Other nations and radio companies followed suit. The first leg of Marconi's new "short wave beam" network was between England and Canada, with its Canadian transmitting and receiving stations near Montreal, at Drummondville and Yamachiche, respectively. The short wave trans-Atlantic service began in October, 1926, and rendered the long wave trans-Atlantic service with its western terminus in Cape Breton obsolete [note 8]. This began a trend toward short wave stations located near urban centres for long distance radio communications, and away from long wave coastal stations with their long land lines. The transmitting station at Chfden had been destroyed in the Irish rebellion in 1922, and its operations were moved to a station near London. Presumably the receiving station at Letterfrack was closed then too. The closing of the Louisbourg station was hastened by a fire that destroyed the receiver building in 1927. The residential buildings were dismantled and used for houses elsewhere. Marconi Towers also ceased being a trans-Atlantic station at this time, but continued providing ship-to-shore services until 1945. The site of Louisbourg station is now a picnic area in the Fortress of Louisbourg National Historic Park.
This is just a thumbnail sketch of the history of the Louisbourg trans-Atlantic receiving station. It says nothing about the people at the station and little about activities at the station during and after the First World War. For example, station plans of this period indicate the erection of other antennas, the purpose of which is unknown. Much more research of primary sources needs to be done to fill out the picture. The author would be happy to receive information about the station, anecdotal or otherwise, or about other sources of information.
Notes and References
1. Practical Wireless Telegraphy, by Elmer E. Bucher, Wireless Press Inc., 1917.
2. Early Radio Wave Detectors, by V. J. Phillips, Peter Perigrinus Ltd.
3. Notes by James Pope, former operator at the Louisbourg station.
4. Notes by an engineer at the Louisbourg station entitled "Explanation of photos of Louisbourg 88-85-17597 to 88-185-17695", in a photo album with SNAPS printed on the cover: Beaton Institute, University College of Cape Breton, Sydney, NS.
5. "Explanations of photos of Louisbourg", ibid.
6. A History of the Marconi Company, by W.J. Baker, Methuen & Co., 1970, page 184.
7. Wireless Over Thirty Years, by R.N. Vyvyan, George Routledge & Sons, 1933, chapter VIII.
8. Several factors contribute to short wave being more practical than long wave for terrestrial long distance radio communications. Reflection of radio waves by the ionosphere is responsible for long distance transmission in both wavelength ranges. However, directional antennas can be built for both transmission and reception at short wavelengths, and these are more efficient than non-directional antennas because most of the transmitted power is beamed toward the receiver. For this reason, Marconi's British Empire radio network was called the "short wave beam" system, or often just the "beam system". Directional antennas are impractical at very long wavelengths because beaming requires that the dimensions of the antenna must be much greater than the wavelength. Short wave also has the advantage of a lower level of atmospheric interference and a greater information channel capacity than long wave. Short wave has the disadvantage of a more variable signal than long wave, but the long term variations are fairly predictable, and can be compensated somewhat by changing the operating frequencies at particular times of the day.
The fact that medium frequencies (MF band) between long and short wave are poor for long distance communications, because of ionospheric absorption of the radio waves, obscured the potential of the still higher short wave frequencies to Marconi and his contemporaries in the early days of radio. Radio waves of even higher frequencies (VHF, UHF, etc.) penetrate the ionosphere and are therefore mainly limited to line-of-sight distances. Marconi investigated transmission at these frequencies in 1916, using a spark transmitter and cylindrical parabolic reflector antennas, with good results.
Beaton Institute, University College of Cape Breton, Sydney, Nova Scotia:
Figures 5, 6, 10, 12, 13, 16, 17, 18, 19, 20, 23, 24, 26, 30.
Canadian Marconi Company, Montreal, Quebec: Figures 18, 27, 28, 29, 3 1.
Fortress of Louisbourg, Louisbourg, Nova Scotia: Figures 13, 22.
GEC -Marconi Limited, Chelmsford, England: Figures 11, 15, 19, 21, 22.
Notman Photographic Archives, Musee McCord, Montreal, Quebec: Figure 4.