Marconi's Wireless Telegraphy: A Unit Study

Today AM and FM radios are often taken for granted — you tune to the desired station, and receive the broadcast, loud and clear. But behind radio reception underlies the principles and challenges that baffled inventors and pioneers in the late 19th and early 20th century. Indeed, modern radio reception is of an entirely different sort than that in the earliest days of wireless.

The Days of Telegraphy

To clarify the difference between radio then and now, in the late 1800s standard broadcasting as we know it today was called “wireless telephony,” an interesting but impossible concept of sending human voice through the air. Since sending the human voice was “impossible,” the focus was on wireless telegraphy, which transmitted the dots and dashes of Morse Code through the air without wires. It was these experiments in wireless telegraphy that rendered such wireless technology as used today possible. Without that technology, there would be no AM or FM radios, no satellite communication, and no wireless cell phones.

How Telegraphy Worked

Early experiments in wireless telegraphy used, almost without exception, jump-spark coils as a transmitter. A jump-spark coil is a large transformer with an attached mechanical oscillator that creates enormous voltages — tens of thousands of volts. Attached to this jump-spark coil is a spark gap. The spark gap creates miniature lightning bolts, and sends the resulting noise to an antenna and to a ground. Undoubtedly, you’ve heard interference from lightning before, and the jump-spark coil creates identical bolts, only on a smaller, more controlled scale. These bolts, when they break down and ionize the air, create enormous electromagnetic fields, which are then transmitted. Radio transmission with such a device was first employed by Heinrich Rudolf Hertz, who used it to demonstrate the unusual properties of electromagnetic fields. With a receiver, he showed how a signal could be transmitted through air. However, he declared there was no practical use for this principle beyond showing how electromagnetic fields work.

However, Hertz’s view on the practical purposes, or lack thereof, of the transmission of electromagnetic fields was challenged. Shortly after Hertz’s experiments, Edouard Branly designed the Branly coherer, a sensitive detector, which acted like a switch when exposed to a transmitted signal. A coherer consists a small glass tube filled with various metallic particles that have the unusual property of suddenly conducting when exposed to an alternating current, but not if exposed to direct current. Hence, the alternating electromagnetic fields sent from a spark-gap transmitter could activate the device. With a coherer and a jump-spark coil transmitter to activate it, Branly created a radio receiver. This receiver worked by using the coherer, a battery, a Morse-printer, and a “tapper.” The coherer’s fillings conglomerated when exposed to a signal from the transmitter. This completed the circuit and allowed current to flow to the Morse-printer, which interpreted each dot and dash from the receiver. The tapper was used to break all the fillings loose from each other in the coherer after a signal was received so that reception could continue. Then, when another signal was received, the process started anew. Thus, wireless telegraphy had its beginnings. It was crude, and short-ranged, but it was a start.

Marconi’s Contributions

Then along came Marconi. He had been interested in such fascinating wireless devices, and had established a small transmitter in his attic. With the help of a coherer, he could ring a bell a few yards away. Later, he attached the receiver to a Morse-printer, and with his transmitter transmitted messages a mile away. Thus, wireless telegraphy was ushered in, and was patented by Marconi in the United States on July 13, 1897.

After sending messages up to ten miles, which was significant at the time, Marconi set out upon the legendary experiment for which he is renowned. Setting up a receiving station in Newfoundland, he waited patiently for days until in Morse-code he heard the letter S sent from across the ocean on December 12, 1901. That he actually received the letter S has been questioned — it might have been atmospheric noise. Either way, he was later sending and receiving messages up to over 2000 miles away, which established beyond a doubt that long distant messages could be sent.

Improvements were steadily made to wireless telegraphy. The most significant one, and the one to which we owe all modern-day wireless communications, is Lee De Forest’s audion: the first vacuum tube. By controlling electrons hurtling through a vacuum, amplification was obtained, creating more sensitivity. But that wasn’t all — the vacuum tube could also be used as an oscillator, replacing the jump-spark coil.

It was soon discovered that by modulating the oscillator’s signal, human voice could be transmitted, which started wireless telephony — leading to our modern AM and FM receivers. Thus, the door was opened to virtually endless possibilities, which in a few years led to that revolution in wireless that changed history — the radio boom of 1920’s, in which the first radio sets for the public were produced — functional, if strange looking and hard to use. The principle was the same as that of wireless telegraphy, and people began to take it for granted that it was quite easy to send signals through the ether. But since that time, the dots and dashes of Morse Code have all but vanished on the airwaves and with them the remnants of wireless telegraphy.

Further Investigation

Guglielmo Marconi
Simple biography from PBS.

Patent US0586193
The patent Marconi filed in the United States for “Transmitting Electric Signals” July 13, 1897. (A similar patent was filed in Britain.)

First Wireless Patent in the USA – 1897
Brief description with picture of replica.

The Case Files: Guglielmo Marconi
“Just who was Guglielmo Marconi? How did he adapt Hertz’s discovery of radio waves to his own work? And how did Marconi’s determination and perseverance factor into his success with wireless telegraphy?” Presentation by Franklin Institute with many interesting primary source documents. If you are short on time, start with Improving Wireless Telegraphy.

Wireless Telegraphy
The “real” story from the IEEE and the United Engineering Foundation.

Who Invented Radio
An interesting discussion of Tesla and patent wars from PBS.

Radio’s First Message
And if it wasn’t Tesla who invented radio, perhaps it was Fessenden? From IEEE.

Marconi Wireless Apparatus
A look at a personal collection of early equipment.

Marconi Receives Radio Signal Across the Atlantic
An incredible achievement at the time.

Marconi’s Wireless Telegraph
An article from McClure’s Magazine published in June, 1899.

Marconi and Wireless Telegraphy
An article from Success published December 2, 1899, dealing with the technology’s adaptation by the U.S. Navy.

Wireless Telegraphy for Inter-Marine Communication
Details of the “wireless plant on board ship,” June 10, 1910.

Activities

Guglielmo Marconi’s Wireless Telegraphy Experiment
Demonstration of wireless transmission. (You may want to install an ad blocker before viewing.)

How to Construct and Efficient Wireless Telegraph Apparatus
Scientific American 1902 supplement. Don’t have a coherer handy? Make your own: Simple Homemade Coherer (The term “simple” here appears to be relative.)

How to Make a Simple Telegraph Set
More accessible to students from Energizer.

Learn Morse Code
In one minute!

Books

Great Inventors and Their Inventions by Bachman
A brief mention in this popular book starts on page 261.

Boys Second Book of Inventions by Baker
A more detailed account in Chapter VII – “Marconi and His Great Achievements – New Experiments in Wireless Telegraphy“.

Manual of the Marconi Institute: For Training in Radio Communications and Allied Vocations
Opportunities in the radio field, training methods, qualifications, recommended reading, equipment and other interesting tidbits.

History of Wireless Telegraphy by Fahie
For older students.

The Radio Amateur’s Hand Book by A. Frederick Collins
Written in 1922, practical guide to everything radio…as Marconi knew it.

Unit Studies

Free Science Studies: Guglielmo Marconi
Part of our science series based on the Bachman book listed above includes further background information, suggestions, and more activities, lessons, and printables not listed here.