Feature Tuning at the Dawn of Radio

chieving precise selective tuning was a key factor in Athe development of radio communication.

To many late 19th century scientists, the discovery of the existence of a vast electromagnetic spectrum, with wavelengths extending from picometres to megametres, was strange and exciting. But in 1888, had seen no practical utility for the radio waves that he had transmitted, received and studied in his laboratory. What use could be made of radiation with these wavelengths longer than heat and light, that could only be detected by instruments? The British scientist William Crookes (of cathode ray and radiometer fame) was an outstanding visionary who saw the future with astonishing clarity. Less than four years after Hertz published his discovery, he envisaged person-to-person wireless communication in remarkable detail, touching on many aspects of the radio art from the ability of the waves to pass through buildings and fog, to coding the messages for secrecy, and using reflecting and dielectric antennas to beam the signals in a desired direction. Marconi’s first tuned transmitter, made at Poole in 1899. The single turn secondary winding couples Remarkably, Crookes also foresaw the the circuit to the antenna. (Image credit: Museum of the History of Science, Oxford). concept of transmitter selection by receiver tuning. In the Fortnightly Review for 1 February 1892, he wrote: “I assume here in Britain using standing waves on open wire narrower bandwidth, and exhibited sharper that the progress of discovery would give transmission lines. Although an eminent resonance effects. He demonstrated these instruments capable of adjustment by turning researcher, Lodge was an amiable gentleman effects during a famous ‘syntonic Leyden jar’ a screw or altering the length of a wire, so as of relaxed character, and when he received lecture to the Royal Institution as early as to become receptive of wavelengths of any news of Hertz’s progress he famously March 1889. preconcerted length. Thus, when adjusted to continued his Austrian vacation, rather than Lodge also went further. In August 50 yards, the transmitter might emit, and the rushing back to England to publish before 1894, during a presentation to the British receiver respond to, rays varying between 45 the young German. Instead, he added a Association for the Advancement of Science and 55 yards, and be silent to all others.” [1] postscript to his own paper complimenting in Oxford, he made what some consider to By contrast, none of the 19 claims made Hertz on his work. Just as with Hertz, Lodge have been the first public demonstration in Marconi’s fundamental 1897 wireless initially had no thought of applying his of practical wireless telegraphy. According telegraphy patent made any mention of discoveries to signalling. But Hertz tragically to his own account, an assistant used a tuning. Nor did the publications of any died in 1894 at the age of only 36, whereas Morse key to send some dots and dashes of the other experimenters in England, Lodge lived until 89, and so he was able to from a spark transmitter in one building to , Italy and Russia at that time. All contribute to the practical development of a coherer receiver in the lecture theatre of the inventors had practical systems of radio wireless for many years. the Clarendon laboratory 55m away, and communication, only so long as there were It was because Lodge experimented with this was later accepted by the US courts very few systems of radio communication. transmission lines rather than radiating as evidence of a demonstration of radio But that was soon to change. antennas that he observed the phenomenon communication at a date prior to Marconi’s of resonance more strikingly. Because of experiments near Bologna in 1895. the radiated energy, a spark transmitter Depending on the interpretation of ‘a Oliver Lodge connected to an antenna generated highly demonstration of wireless telegraphy’, this While Hertz was making his studies of damped waves that had a broad spectrum, priority claim remains a contentious issue. electromagnetic waves radiated in free whereas the less damped waves that it In a lecture to the Royal Society of Arts in space, Oliver Lodge was doing similar work excited in closed tuned circuits had a 1937, Ambrose Fleming stated that it was 26 September 2018 Feature

unquestionable that Lodge had pre-empted when Marconi and others started claiming Today, this idea is so familiar to everyone Marconi by demonstrating electric-wave property rights in discoveries to which he had who has used a radio receiver that it may seem telegraphy at that time. But in her touching contributed. On 10 May 1897 he applied surprising that it was not at all obvious at the and imaginative biography of her father, for what was to become recognised as the time. But the patent had major implications Degna Marconi changed ‘unquestionable’ to basic radio patent on tuning. This described a for the design of future transmitters, receivers ‘questionable’ [2]. complete system of wireless telegraphy, but so and antennas, and it became increasingly had Marconi’s patent of 1896. The difference valuable as the radio spectrum became was that Lodge specifically described a system more and more crowded. In Lodge’s original Basic tuning patent in which transmitter and receiver could be description only the antenna circuits were Initially Lodge was reluctant to file patents, tuned to a particular frequency, and so could resonant, so the selectivity was limited by as he considered his scientific discoveries operate in the vicinity of other transmitters the fact that they were open tuned circuits public property. But he felt that he had to act operating on different frequencies. coupled to free space. Resonance was achieved by adjustable antenna tuning coils at the feed point, and the receiving antenna was coupled to the detector by a high General principle of the Marconi multiple tuner, omitting the fixed frequency transformer, also a very important capacitors, range and standby switches, and antenna protection. (Image innovation in electronics design. credit: Museum of the History of Science, Oxford). Surprisingly, despite Lodge’s earlier observations about their narrower bandwidth, there were no other closed tuned circuits in the transmitter or receiver configurations he described. (The secondary circuit of the receiver transformer wasn’t tuned to resonance). Equally strangely, he didn’t show a high frequency transformer for coupling the transmitter to its antenna. Since only the antennas were resonant in his system, Lodge discouraged the use of antenna designs that worked against ground, such as the quarter- wave vertical. Except in a few special cases, such as the ground of a ship’s hull in sea water, he considered that the properties of the ground connection were too uncertain for accurate tuning.

Perfect interference The growing need for selective tuning became very apparent during the evaluation tests of radio equipment carried out by the US Navy in 1899 [3]. Having noted the very successful operation of Marconi’s system during the reporting of the America’s Cup Fleming’s cymometer absorption wavemeter used a 1m long coil and tubular variable capacitor with a yacht races in September and October, naval common slider. observers invited him to allow his equipment to be tried out between the cruiser New York, the battleship Massachusetts, the torpedo boat Porter, and a shore station at the Highlands of Navesink, overlooking the entrance to New York Bay. Marconi was initially very reluctant to agree to these tests, on the grounds that he had brought only short-range equipment to the US for the races, and that it didn’t incorporate the latest improvements. Nevertheless the tests were very satisfactory, except for the crucial fact that communication proved impossible if the shore station transmitted while one ship was

The standard 1907 Charles Franklin multiple tuner covers 80 to 2600m in 4 ranges. The large Dr Bruce Taylor, HB9ANY terminal on the left is a protective micrometer spark gap. (Image credit: Alayne Alvis, Museums [email protected] Victoria, Melbourne).

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and manufactured radio equipment for its own use, some of which involved definite infringements. When the Marconi Company attempted to secure compensation for patent infringement from the US Government, the Supreme Court declared its tuning and valve patents invalid.

Four 7s patent The master tuning patent No 7777 granted to Marconi on 26 April 1900 is one of the most famous in radio history. This ‘Four 7s’ patent was the subject of more litigation than any other, bar Lodge’s basic tuning patent itself and the thermionic valve patents of Lee de Forest. The essential difference from Lodge’s The ‘intensifier’ control on the right side of the multiple tuner rotates the coils in the ganged disclosure was that after much trial and error, variocouplers. (Image credit: Museo Nazionale della Scienza e della Tecnologia, Milan). rather than by theoretical analysis, Marconi had obtained better results with two tuned circuits at the transmitter and two at the receiving from the other. In the words of the was also somewhat secretive about how receiver. In addition to the tuned antennas US Navy historian, Linwood Howeth, “The the system actually worked. Despite this, described by Lodge, he used a closed tuned results of the interference tests were perfect. the Navy offered to purchase twenty sets exciter circuit in the transmitter and a closed That is, the interference was perfect.” of wireless equipment, but Marconi refused tuned detector circuit in the receiver, each According to the files in the Marconi to sell outright and offered to lease the coupled to its antenna by a high frequency archives, the spark gaps in the transmitters equipment instead. This was not acceptable transformer that he called a ‘jigger’. and the coherers in the receivers were to the Navy, so he failed to secure a contract. With an appropriate turns ratio the jigger connected directly between antenna and The US Navy Department often showed also increased the sensitivity of the receiver, ground, so that the transmitted signals were rather scant regard for intellectual property by improving the match between the low very broad and the only selectivity was issues, and sometimes arranged for small impedance at the antenna feed point and the provided by the antenna length, which was US companies to make lower cost replicas high impedance of the detector. (Adolf Slaby, much shorter on the small torpedo boat than of individual items of wireless equipment the German pioneer who was probably the on the larger vessels. Marconi told the Navy’s that it had evaluated. These items were first to recognise this problem, tackled it by Radio Telegraph Board that he was unable then put together by its own technicians to inserting a quarter wave line between the to demonstrate his tuning apparatus because make composite systems that they installed two points). The transformer coupling was it hadn’t yet been patent protected, and he in their ships. The US Navy also designed loose, so that the resonance curves remained sharp. This ‘four circuit’ tuning system was novel, but it was based on the tuning concept that had previously been patented by Lodge, and Marconi’s patent was weakened by the fact that it included the essential elements of Lodge’s earlier claims. Marconi soon appreciated the improvements in range that were obtained by using tuned circuits to improve the sensitivity of his receivers, and to concentrate transmitter power in a narrower bandwidth. But it is interesting to note that it was only with an untuned receiver that he heard the three dots from Poldhu at Signal Hill in Newfoundland in December 1901, not with the tuned set which he also tried. This might have been because the transatlantic signal that he received was actually unintended high frequency radiation from the quenched spark transmitter at Poldhu. For it is most unlikely that the fundamental signal (estimated to have been somewhere between 150 and 990kHz) would have been detectable at such range over a daylight path. [4] Marconi and other experimenters had only approximate ideas about the frequencies of A calibration chart was provided to allow the wavelength to be read from the intermediate tuning their transmitters until Fleming invented condenser. (Image credit: Museum of the History of Science, Oxford). the cymometer in 1904. This instrument 28 September 2018 Feature

tuned by solid dielectric variable capacitors of his own design. The 4mH antenna tuning coil had 20 switched taps, and the input was protected by an adjustable spark gap, as well as a choke providing a DC path to ground. The aerial circuit was coupled to the detector circuit via a high-Q intermediate circuit having ganged input and output variocouplers, which could be adjusted by an ‘intensifier’ control on the right side of the case. The unit could be switched from the ‘Tune’ mode for normal selective operation to the broadband ‘Stand Bi’ mode when awaiting strong calls on an unknown wavelength.

Other experimenters Meanwhile many other experimenters, such as Ferdinand Braun in Germany, and Nicola Tesla and John Stone in the USA, devised other coupled circuit arrangements to achieve similar results. Stone even proposed an ‘eight circuit’ system with three closed tuned circuits at transmitter and receiver, and claimed that in that case it wasn’t essential for good selectivity that the antennas be resonant, although it facilitated impedance matching. In fact, non-resonant antennas must have been used by Marconi when he demonstrated the tuning by sending messages simultaneously from a pair of transmitters on the Isle of Wight to a pair of receivers at a station in Dorset. Since they operated on different wavelengths there was no mutual interference, even though the same antennas were shared by both transmitters and by both receivers. Considering that Marconi had never The antenna tuning coils of station GBR at Rugby were wound with Litz wire cables of 6561 strands collaborated with Braun, and indeed had been of 36swg copper wire. (Image credit: British Telecom). involved in an acrimonious patent dispute with him, it was surprising that they were awarded the 1909 Nobel Prize in Physics was a form of absorption wavemeter, with a metres, and is said to have won a £5 bet with jointly. 24 years later Marconi related that on sliding handle that allowed the capacity and Marconi, who expected that the tests would the train to Stockholm Braun suggested that inductance of its tuned circuit to be varied fail. they play cards for each other’s half share of simultaneously and in the same proportion. Franklin’s standard multiple tuner was a the prize, but “I was such a poor card player Resonance was indicated by the brightness of very adaptable and beautifully finished unit, that I declined.” [5] a neon indicator tube. Later Henry Round and which was hand built in quantity at Marconi’s others produced more compact wavemeters Chelmsford factory. It covered 80 to 2600m in that covered a wider frequency range. Fleming, four switched ranges, and had three circuits who never suffered rivals gladly, complained to Marconi that “these young men read my books and then pretend to make inventions.” A classic transmitter tuned In 1907 Charles Franklin, one of Marconi’s circuit made by long standing research associates, designed Marconi in Genoa. and patented a multiple tuner that became The capacitor is the standard equipment for use with magnetic Leyden jar on the detectors for many years. Franklin was a left, and the coupling prolific inventor who later designed the between the windings transmitter for the BBC station 2LO, and of the jigger (antenna whose last assignment was the antenna and coupler) is adjustable. feeder system for the television transmitter (Image credit: Museo at Alexandra Palace. He even successfully Nazionale della Scienza e demonstrated short wave communication della Tecnologia, Milan). between London and Birmingham on 15 30 September 2018 Feature

An early tuner with tapped inductor, probably built by the Italian Navy Arsenal in La Spezia, which had free use of Marconi’s patents. (Image credit: Museo Nazionale della Scienza e della The huge jigger of the 300kW synchronous spark transmitter at Caernarfon in North Wales. (Image credit: Tecnologia, Milan). Wireless World).

Consolidation Now armed with both tuning patents, When Marconi and other manufacturers Marconi successfully attacked United began using his inventions freely, Lodge Wireless, the major North American didn’t immediately defend his patent rights operating company that used de Forest by suing for infringement. He thought apparatus. In 1912, when United was that litigation would be time-wasting and unable to pay the damages awarded, expensive, and felt that it was incompatible Marconi took over that company, with with the moral principles of a scientist. But its 70 shore stations and 500 shipboard in 1911, he secured an extension to his installations. A similar infringement suit put tuning patent on the grounds that he had the National Electrical Signalling Company received almost no compensation from it out of business, leaving American Marconi during the initial term, and he finally filed a in a dominant position in the US. In Europe, suit against Marconi. admitted infringement of Lodge’s The Marconi Company entered a tuning patent, and was obliged to join with countersuit, but feared that they might the Marconi Company and its European lose the court battle, since Lodge’s tuning licensee in an international consortium, patent could well be considered the parent which took control of German and later of their Four-7s one. Invalidation of that Austrian marine radio until the start of WWI. patent would have been a severe blow to In June 1943, the US Supreme Court A Townsend wavemeter with variometer tuning a manufacturer that needed a strong legal invalidated Marconi’s Four 7s patent. But and switchable fixed capacitors. Resonance was base to challenge competitors in the US and it upheld Lodge’s 1897 one, judging it to indicated by a neon lamp. (Image credit: Museo Germany, and which would certainly be be fundamental to every radio system in Nazionale della Scienza e della Tecnologia, scrutinised by a parliamentary committee existence that used tuned circuits. Three Milan). when it sought a major contract to build the years after his death, the amiable researcher Imperial Wireless Chain. who found the very idea of registering a Although he had previously crossed patent claim repulsive, and inappropriate [3] L S Howeth, History of Communications- swords with both sides on other minor for a public-spirited scientist [6], was finally Electronics in the United States Navy, Govt issues, the man who brokered a peaceful recognised as having fathered the invention Printing Office, Washington, 1963, pp 28-36 solution to this dilemma was William from which all other radio tuning systems [4] J S Belrose, A Radioscientist’s Reaction to Preece, who as chief engineer of the GPO were derived. Marconi’s first Transatlantic Wireless Experiment - had supported Marconi’s early wireless Revisited, Proc 2001 IEEE Antennas & Propagation experiments in Britain. The Marconi Society International Symposium, Boston, Vol. 1, Company was accustomed to litigation, References pp 22-25 but Lodge had no desire to enter a bitter [1] W Crookes, Some possibilities of electricity, [5] M Raboy, Marconi, Oxford University Press, conflict. On 21 October 1911 he agreed The Fortnightly Review, 102, 1 February 1892, 2016, ISBN 9780199313587, p 305 to sell his patents to Marconi and accept a pp 174-176 [6] O J Lodge, Signalling across Space without nominal position as scientific advisor to the [2] D Marconi, My Father, Marconi, Guernica Wires, Third edition, The Electrician Publishing company, with an annual stipend of £1000. Editions, 1996, ISBN 9781550710441, p 21 Co, 1900, p 51 32 September 2018