Communication Receivers 1:“ Looking back at the earliest years and genesis of the Radio Experimenter

While researching the early days of wireless (the word "radio" was not used until after 1908), one realises that the innovation and intellectual power applied to address the challenges of the time was as great as the present day. Time has offered essentially only much greater volumes of data and choices. An example of such early literary published work was by J.A Fleming who published "the Principles of Electric Wave Telegraphy" in 1906. It is interesting to realise that the earliest of wireless communication was the application and natural evolution of the theoretical laws of physics as understood at that time, which today is simply high school physics. Guglielmo Marconi was the first to practically demonstrate and commercialise wireless communication. The following chronology of events is as follows: 1896 - Marconi demonstrates the wireless telegraphy to the English telegraph-office, after a year of testing in Italy with a coherer. He filed his patent in on June of that year. 1897 - Marconi establishes the first "Marconi-station" at Needles (Isle Wight), this station sends a signal to the English coast over 22 km. 1898 – On 3 June, the first paid wireless telegram sent from Needles. On the 20 July, the first newspaper message was sent from a ship to the Daily Express concerning the results of a sailing contest. 1901 - On the 12 and 13 December Marconi uses syntonised (tuned) receivers and transmitters to send and receive the first signals sent across the Atlantic Ocean from Poldhu to New Foundland

Marconi also established a wireless transmitting station at Marconi House, Rosslare Strand, Co. Wexford in 1901 to act as a link between Poldhu in Cornwall and Clifden in Co. Galway. He soon made the announcement that on 12 December 1901, using a 152.4-metre (500 ft) kite-supported antenna for reception; the message was received at Signal Hill in St John's, Newfoundland (now part of Canada) signals transmitted by the company's new high-power station at Poldhu, Cornwall. The distance between the most distant two points was about 3,500 kilometers.

The Marconi station at Clifden in Galway

Before addressing the reception of signals it is appropriate to understand the earliest generation of radio signals or radio waves for communication purposes using telegraphy. In 1901 Marconi in a lecture to the Society of Arts, explains the principle of "Syntonic Wireless Telegraphy". Marconi describes that signals from two different transmitters interfere with each other and are to distinguish and by using tuned circuits he is able to resolve them individually. Articles by many authors followed. Similar articles are; "Syntonic Wireless Telegraphy" by G.M Hopkins published in "experimental Science" in 1902 and William Mayer Jr in an article titled "Wireless Telegraphy Today" in The American Monthly Review of Reviews in 1904.

The induction coil as used by Tesla and Rumkorff to generate high voltage sparks and electric discharges in the air was the device used by Marconi to generate oscillating waves. The earliest transmitter made use of a spark generated by this induction coil I, similar to an ignition coil in a motor car, connected to a battery B which was interrupted by vibrating contact, which emulates an alternating current frequency. The telegraph key K is used to transmit a coded signal using Morse code. The spark generated across the spark gap b b is rich in harmonics and is transmitted from the antenna wire A which has a resonant frequency. A condenser or capacitor was added to the induction coil forming a tuned circuit and used the energy in the spark to sustain "radio frequency" oscillation in the form of damped or decaying oscillations for about 50 or 60 cycles. The interrupter frequency was about 2000 cycles per second. This produced the pronounced "chirp" of a spark transmitter. The actual frequency of transmission was the determined by tuned circuit the inductance spark coil and capacitance across it.

The induction coil interrupter was later replaced by high frequency alternators. Spark quenchers were also used to stabilise the spark oscillation. The early transmissions were in the medium and long wave bands from about 80 to 2500 meters The Earliest Receiver The most basic receiver of radiated waves as first used by Marconi and others is shown in Fig 2

The detector of the radiated waves used the filings coherer k, which based its operation on the fact, that when metal filings are packed loosely together and make part of an electric circuit they have a normally high electrical resistance, but in the presence or under the influence of electrical oscillations this resistance reduces and they become conductors of an electric current. It was assumed that the electric oscillations cause the filings to cohere more closely together, thereby making a better contact with one another; hence the term coherer was applied to this form of electric-wave detector. It was further noticed that when the filings had cohered they retained their electrical conducting property even after the cessation of the oscillations until they were tapped or otherwise jarred, and they resumed their normal high-resistance condition. Therefore, to make this device operative, a means of jarring the filings continuously to restore them to normal condition was necessary, and this was easily found in the shape of a vibrating bell or "tapper" T, the hammer of which was caused to tap the tube containing the filings. The detected signal in the form of a pulse drove the relay R known as a Morse sounder and the detected signal could be heard as clicks. The detected signal also could also drive an inker E and the Morse Telegraphic message was read off a paper tape. Thus is the basis of the rectifier or diode detector as we know it today. The first practical Communication Receiver Marconi’s invention of the magnetic detector in 1901 was particularly important an is known as the Cymoscope shown below.

The two wooden discs ee are grooved around the edge and are driven around slowly by a clockwork mechanism. An endless band a of fine silk covered iron wires are arranged, as a belt, in the grooves moving at a rate of 7 to 8 cms per second. The iron band passes through a glass tube gb on which a coil of insulated wire is wound connected between the aerial A and the earth E. The secondary coil c is wound over this coil connected to a telephone earpiece T or a telegraph inker or sounder. The horseshoe magnets dd are arranged such that similar poles are together over the coils. As the iron wire rotates a portion of the wire is magnetized by the first magnet and due to the magnetic retentivity or hysterisis of magnetized iron that portion is shifted forward in the direction of rotation. If an electric current from the aerial passes through the coil gb the field created annuls the hysterisis of the iron and this magnetized portion moves back to a position opposite to the magnetic poles. This amounts to a magnetic pole moving through the coil c, connected to the telephone which makes a sound for the duration of the electrical oscillation through the coil gb connected to the aerial. The magnetic detector was connected to a tuner of coils (inductors) and capacitors which selected the frequency transmitted as shown below

The diagram of the early Marconi tuner is shown below an together with the magnetic detector made up the first commercial communications receiver of the time.

There were many developments to make the detector more sensitive and reliable, among them the Solari mercury autocoherer, used by the Italian navy; the Marconi and other magnetic detectors; the De Forest electrolytic detector; the Fessenden "heat" detector, and the Lodge-Muirhead oil-film detector. Each of these electric-wave detectors, or, more correctly, electric-oscillation detectors, while differing more or less in principle, effect the same final result,--that is, they either produce or vary a current in a local circuit in which is placed a telegraph relay or a telephone receiver, or they vary the resistance of that circuit and thus cause the relay or telephone to respond to the received signals. Many new innovations are driven by the needs of war. As Marconi had patented his wireless telegraphy system in 1896 it was Sir William Preece, Chief Engineer of the Post Office that invited the British War Office, with Marconi, to a demonstration of "communication without wires". The Royal Engineers who were responsible for all military signalling at the time were instructed to monitor the progress at the time but no orders were placed or further interest was forthcoming. Marconi however had to wait three years to prove the system in a military context by installing apparatus in three Navy ships Juno, Europa and Alexandra for the duration of summer manoeuvres. The antenna the only frequency determining element was 52m of wire attached to the top masts achieving a range of 186km. After this the use of wireless on ships for ship to shore port communications was readily accepted. At this time in South Africa the ZAR (Zuid Afrikaanse Republiek) and the British Empire were in conflict which was the prelude to the Anglo Boer War. In 1898 Mr C.K. Van Trotsenburg; General Manager of Telegraphs in the ZAR advised the military of the ZAR on the possible use of "wireless" telegraphy. In February 1998 he contacted Siemens Brothers of London (subsidiary of Siemens and Halske of Berlin requesting equipment to link a number of forts around Pretoria in the ZAR. In August 1899 on approval from ZAR government Van Trotsenburg placed an order for six "vonkentelegraafinstrumenten" (spark telegraph instruments)" In 1899 President Kruger of the ZAR demanded that the British troops withdraw from South Africa and declared war. Despite all precautions the shipment arrived after the declaration of war and after having arrived in Cape Town was confiscated by the British customs authorities. Had the war broken out a few months later allowing the system to be installed and the ZAR would have been the first in the world to have a network of wireless telegraphy posts available for military purposes.

After this event Marconi lost no time in advising the British to use his wireless apparatus, for ship to shore communications in Durban and Cape Town. A 6 month contract to hire 5 wireless sets and 6 Marconi Engineers was commenced in November 1899. However on arrival the local military authorities invited the Marconi engineers to volunteer and accompany the army into the field. As the equipment was designed for use on ships considerable modifications were needed to make them mobile and field worthy and were only partially successful. Marconi announced that these trials had "no bearing on the practicability under normal conditions". As a result Marconi further developed various field Wireless sets, one of which is illustrated below.

One of the events that still capture’s the imagination the modern world is the tragedy around the sinking of the Titanic. The radio station as used on the Titanic was a Marconi Syntonic System. The receiver was a Marconi Tuner with a magnetic detector. The transmitter was a 5 kW rotary spark transmitter which, with the 4 wire antenna suspended 250 feet above sea level between the ship's masts, had a range of up to 400 miles during the day and up to 2000 miles at night. An example of the station is shown in the picture below

In the early 1900’s, almost every developed nation had developed one or more systems of wireless telegraphy. In the United States there were the De Forest and Fessenden systems; in Great Britain, the Marconi and Lodge-Muirhead systems; in Germany, the Slaby-Arco and the Braun systems, later known the Siemens-Halske wireless system; in France, the Ducretel and in Italy the Marconi wireless method was used. In Russia, the Popoff system was used; while in Japan a wireless system was also developed at the time. Examples of some these developments and the scale of the developments are shown below.

Early transmitters used oil engines to drive alternators to generate wireless electric oscillations

The alternator was synchronised with the spark discharger to ensure reliable operation

Alternators were manufactured to produce frequencies of up to 20,000 cycles per second to energise 200kW spark gap arc circa 1920

The high energy sparks were controlled by dischargers or spark quench components but remained spectrally noisy. Spark transmitters although were used by some ships used the till WW2, but the large transmitting stations were replaced in 1920s. The challenge to Marconi’s patent The story of Marconi is not complete without a mention of the challenge of who actually invented the radio. While most people will credit him with commercialising the invention there were other players of the time that contributed intellectually through experiments and demonstration. Notably Bose, Lodge, Tesla, Popov, Stone and others. These are well documented in the following link: http://en.wikipedia.org/wiki/Invention_of_radio In 1943, a lawsuit regarding Marconi's numerous other radio patents was resolved in the United States. The court decision was based on the prior work conducted by others, including Nikola Tesla, Oliver Lodge, and John Stone from which some of Marconi patents stemmed. The U. S. Supreme Court stated that, The Tesla patent No. 645,576, applied for 2 September 1897 and allowed 20 March 1900, disclosed a four-circuit system, having two circuits each at transmitter and receiver, and recommended that all four circuits be tuned to the same frequency. [... He] recognized that his apparatus could, without change, be used for wireless communication, which is dependent upon the transmission of electrical energy. In making their decision, the court noted; "Marconi's reputation as the man who first achieved successful radio transmission rests on his original patent, which became reissue No. 11,913, and which is not here [320 U.S. 1, 38] in question. That reputation, however well-deserved, does not entitle him to a patent for every later improvement which he claims in the radio field. Patent cases, like others, must be decided not by weighing the reputations of the litigants, but by careful study of the merits of their respective contentions and proofs." The court also stated that "It is well established that as between two inventors priority of invention will be awarded to the one who by satisfying proof can show that he first conceived of the invention." Finally on 21 June 1943, the Supreme Court of the United States credited Nikola Tesla as being the inventor of the radio. The Genesis of the wireless experimenter During these years the regulations around radio communications was a matter of record of apparatus and application, formal regulation was only established in 1912. Wireless communication fascinated the curious and amateur experimenters followed and the radio amateur hobby was born. A detailed description of "Apparatus for Wireless Telegraphy" was published by Prof Jerome J. Greene in the "American Electrician in July 1899". Further Evidence of information on how to build a wireless system was in an article from "Experimental Science, G.M. Hopkins, 1902" by A. Frederick Collins; "How to construct an efficient wireless telegraph apparatus at a small cost". There are few records of amateur experimenters during this pre-regulation period. In 1910 the first national radio society in the world known as the WIA, The Wireless Institute of Australia was formed. It was quickly followed in the spring of 1911 by the foundation of the first Wireless Club of Great Britain in Derby, near London and renamed the RSGB in 1922. The American ARRL was started in 1914. In 1911 the publication known as "Modern Electrics" printed 52,000 copies of this magazine. There were 10,000 amateurs in the USA, as many or almost in the United Kingdom and probably as many in gathering all other countries together. In 1999 a well preserved station was uncovered by Henry Rogers WH7HTR in the USA. It was owned by Marion Henry Dodd who operated his station from 1912. The station is shown below andl described on the website http://www.radioblvd.com/DoddStation.html dedicated to this discovery.

All the apparatus he used is "state of the art" of the time similar to the Marconi Syntonic System described in this article. Wireless experimenters continued to follow developments of the spark transmitter and improved detectors till the end of the second decade of the 20th century. Many new developments led by the needs of the first world war and the golden era radio of the 1920s which will be subject of part 2 of Communications Receivers.