So many years ago (January 2005), I was approached to put together a website about the Marconi Towers. This was after a presentation I attended titled - Nova Scotia's Wireless Communications Heritage: Is it worth saving?.
The website I created was online for a very short period of time, and then recently the local IEEE Section has been working on getting a milestone marker and I remembered that I have a RAR archive with a bunch of great information.
Henry Bradford wrote about the Three Marconi sites in 1996 and the article was published in the Royal Nova Scotia Historical Society Journal in Vol. 1 1998. It is reproduced here.
The information below is everything that I have found, so far, that I have on my archive drive from that time.
In the early years of the twentieth century, Guglielmo Marconi, the famous radio pioneer, built powerful radio stations on both sides of the North Atlantic Ocean to achieve his goal of a transatlantic wireless telegraph service. In the course of developing transatlantic wireless from the experimental stage to a commercial service, the Marconi Company built three stations on Cape Breton Island in the Canadian province of Nova Scotia, and corresponding stations in Great Britain to communicate with them.
The Cape Breton stations were at Table Head in the town of Glace Bay, at Marconi Towers on the southern outskirts of Glace Bay, and at Louisbourg on the Atlantic coast about twenty-five kilometres south of Glace Bay.
These were long wave radio stations, operating at wavelengths of thousands of metres. The service operated until 1926, when it was replaced by short wave stations near London and Montreal. This website provides a pictorial description of the three Cape Breton stations with explanatory text. Its purpose is to provide an on-line archive of the many photographs of the stations. These include both historical photographs taken when the stations were operating, and recent photographs of the station sites and commemorative events.
Hertz And Radio Waves
In the period covered by this website, “radio” means wireless communication by means of radio waves. Radio waves are invisible electromagnetic waves that travel through the air or empty space at a speed of three hundred million metres per second, commonly referred to as “the speed of light”. The three main components of a radio system are the transmitter (including its antenna), the receiver (including its antenna), and the radio waves that carry messages from the transmitter to the receiver.
The existence of electromagnetic waves was predicted by James Clerk Maxwell’s electromagnetic theory, developed in the 1860’s. We now know that X-rays, light, and radio waves all are electromagnetic waves. What distinguishes them from one another is their wavelength; i.e., the distance between successive peaks of the wave. Light has a wavelength of about one millionth of a metre. The term “radio wave” is applied to waves with a wavelength ranging from about one millimetre to many kilometres.
In the 1880’s, Heinrich Hertz performed a classic series of laboratory experiments to measure the properties of electromagnetic waves. He chose a wavelength of about a metre so that he could generate several complete waves within the confines of his laboratory at any instant. Hertz generated these waves by means of electrical oscillations in a dipole antenna. The oscillations were produced by electrical impulses created by high voltage electric sparks. Initially the waves were called “Hertzian waves”, but later they became known as radio waves.
To detect the radio waves, Hertz set up a second dipole antenna a few metres away from the first. It was connected to two electrodes separated by a small gap. When the radio waves struck this second antenna, a small electric spark appeared in the gap. Hertz’s radio wave generator and detector might be regarded as the first primitive radio transmitter and receiver; at least the first ones that worked on clearly understood principles.
Marconi’s Radio Experiments; The Spark Transmitter
In 1894, a young Italian, Guglielmo Marconi, read about Hertz’s experiments, and reasoned that radio waves would be an ideal medium for wireless communications. Making this inspiration a reality became his life’s work. Marconi did not have the field to himself. There were competitors in several countries, including such names as Braun (with whom he later shared the Nobel Prize for wireless work), Lodge, Popov, and Fessenden, to name a few.
In 1895, Marconi modified Hertz’s apparatus to transmit radio waves over longer distances. At both the transmitter and receiver, he replaced Hertz’s small dipole antenna with a combination of a tall vertical wire (the “aerial”) and a connection to the ground. In the receiver, he replaced Hertz’s small spark gap by a radio signal detector called a “coherer”. The coherer received its name because it contained a metal powder that cohered when a radio signal was impressed on it. The coherer acted like a voltage-controlled switch that actuated a paper tape recorder when a signal was received.
Like Hertz, Marconi used a high voltage electric spark to produce radio frequency oscillations in the antenna. This type of transmitter became known as a “spark transmitter”, and radio operators were often nick-named “Sparks”. Messages were transmitted in Morse code by switching the transmitter on and off with a telegraph key. With this apparatus, Marconi transmitted radio signals about two kilometres on the family estate near Bologna, Italy in 1895. Many consider this achievement to be the birth of radio.
Development Of Commercial Wireless
Marconi moved from Italy to England in 1896, and founded a company in 1897 to manufacture and sell wireless equipment. His principal customers were shipping companies because ships needed wireless communications, whereas on land the industrialized nations were well served by land line telegraph networks. In addition to equipping ships with radio, the Marconi Company built chains of ship-shore stations along the coasts of Great Britain and North America.
Two major improvements were made to spark radio systems during the early 1900’s. The first was to couple the transmitters and receivers to their antennas via radio frequency transformers instead of connecting them directly. This greatly improved the tuning by removing the energy absorbing spark and coherer from the antenna circuits. The second improvement was the replacement of the coherer by more sensitive detectors. The best detection arrangement was eventually found to be the combination of a crystal diode detector and headphones. The main advantage of this arrangement was that it utilized the great sensitivity of the human ear. Systems of this type were the mainstay of radio communications until about World War 1 (1914-1918).
Marconi and others found that the taller they made their vertical wire antennas, the greater the distance over which they could communicate. One reason was that, at the long wavelengths being used, the voltage of the received signal is proportional to the height of the receiving antenna. Another factor was that taller antennas resonated at longer wavelengths or lower frequencies. (Frequency is inversely proportional to wavelength). This increased the range of the transmissions because the ground or water over which the waves travel absorbs less energy from the waves at low frequencies.
The trend toward lower frequencies and longer wavelengths continued for several decades. By the early 1900’s, the frequencies in use had decreased about a thousand times from those used in Hertz’s experiments, from hundreds of megahertz down to hundreds of kilohertz. In the course of this downward shift in frequency, the long distance capabilities of frequencies in the range of roughly 3 to 30 MHz were overlooked. This band is now known as the “high Frequency” (HF) or “short wave” radio band. The ability to communicate over long distances at short wave frequencies was only fully appreciated when more sensitive receivers with vacuum tube amplifiers became available after World War 1 (1914-1918).
By about 1900, Marconi had discovered that signals from his larger stations could be received hundreds of miles away, indicating that low frequency radio waves did not travel in straight lines as most scientists expected. Straight line propagation would have limited them to horizon distances. Instead, they apparently followed the curvature of the Earth due to electrical interaction with the ground or water over which they travelled. This suggested that bridging the Atlantic by radio should only be a matter of constructing transmitters of sufficient power and receiving antennas of sufficient size.
Marconi Bridges The Atlantic With Wireless
In 1901 Marconi decided to attempt transatlantic communications between high powered stations that he had built at Poldhu, Cornwall, England, and Cape Cod, Massachusetts, USA. Unfortunately, gales wrecked the antennas at both stations in the fall of 1901, so Marconi carried out his transatlantic experiment with a temporary transmitting antenna at Poldhu, and portable receiving equipment at St. John’s, Newfoundland. The station at Poldhu was instructed to transmit a test signal consisting mostly of the three dots of the letter “S” in Morse code, repeated over and over for a few hours near midday at St. John’s. This test was carried out for a few days in December, 1901. Marconi claimed to have received the signal several times on December 12 and 13.
This claim is surrounded by much controversy because subsequent experience has shown that transatlantic propagation at the claimed wavelength of 366 metres (820 kHz) is nearly impossible in the daytime. If the test signals really were received, it most likely was at short wave frequencies. This is suggested by the fact that Marconi was unable to receive the signals with a receiver tuned to the expected frequency, but apparently received them with an untuned receiver. The short wave explanation assumes that although the Poldhu transmitter was tuned to around 820 kilohertz, it was also transmitting significant energy at short wave frequencies. This is quite possible because the spectra of the early spark transmitters were notoriously broad. Whatever the explanation, the Newfoundland experiment served the useful purpose of encouraging Marconi to continue on to eventual success. If the signal really was received at short wave frequencies, the great potential of short wave radio had been missed by attributing the success to the wrong frequency band.
Some of these uncertainties were cleared up In 1902 when Marconi installed a receiver, tuned to 366 metres once again, on the liner SS Philadelphia making a voyage from England to New York. He received signals from the Poldhu station, recorded on paper tape, farther than the transatlantic distance in the Newfoundland experiment, but only at night. During the day he could only receive signals at less than half that distance. Although these results left the Newfoundland achievement shrouded in questions that never can be answered definitely, they verified that transatlantic wireless communications were possible. This was confirmed again in the summer of 1902 on a transatlantic voyage by the Italian navy cruiser Carlo Alberto. On this voyage, Marconi received radio signals from Poldhu right into the harbour at Sydney, Nova Scotia, Canada, but again only at night.
Prior to this voyage, Marconi had announced in December 1901 the successful receipt of transatlantic radio signals at St. John’s. When the company that had a monopoly on telegraph operations in Newfoundland heard this, it demanded that he cease operations there. To avoid legal wrangling, Marconi packed up and left Newfoundland December 24, and disembarked at North Sydney, Nova Scotia to catch the train to New York. There he was met by alert Canadian officials who had been following his progress in Newfoundland. They convinced him to stay in the area and look at potential sites for a permanent station. He chose a promontory called Table Head overlooking the Atlantic Ocean in the bustling coal mining town of Glace Bay. This became the site of the first of three large radio stations that he built in Cape Breton Island, Nova Scotia, in his quest to establish a commercial transatlantic wireless telegraph service. This website tells a pictorial story of these stations.
This post is part 1 of the "History - Marconi In Cape Breton" series:
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