Growth of Radio Communication

Radio Record, Volume III, Issue 6, 23 August 1929, Page 3

Growth of Radio Communication

ADIO is younger than the average reader. Within 30 years it has developed from doubtful experiment to a world-wide necessity. It is becoming more than a daily amusement, it is moulding the destiny of civilisation and it is not speculation to say that within the next 20 years communication, both verbal and visual, will be taking forms that the mind cannot picture. The following is the synopsis of an address on this topic delivered to the Wellington Radio Society by our Technical Editor.

S early as 1838 the first wireless telegraphic signals were transmitted, when Steinheil 1 was conducting experiments in transmitting wireless tele--es graphic signals through iron railings, On the completion of the experiment it was found that in more than one place the railings were not touching, and it was realised that such -@ phenomenon as wireless telegraphy was possible. In the latter part of the nineteenth ceyéury a brilliant young scholar who was to specialise in mathematics became well known at Cambridge Uni-versity-this was the now world-famed Olark Maxwell. Working from a hypo‘thesis, Maxwell proved mathematically that wireless telegraphy was possible and that it took the form of waves which could: range up ‘to’ 100. miles long. These had the power of penetrating and could be reflected. He ad- , vanced: the theory. that when a flucof electricity. took place in a magnet, a series of surges was set up in the field of this magnet. These surges moved at a definite number per second, and-were' consequently a definite distance apart, and that if an instrument could be devised to move in harmony with these, signals could be. transmitted without wires. Considerable interest was aroused by ~ _ these rather startling hypotheses, and in 1887 the attention of a German scienist, Hertz, was drawn to these _ publications. He was sent to England to prove or disprove Maxwell’s theories. In his experiments he constructed an induction coil which fed high-tension impulses to two balls of. metal, and at a distance of some 20 or 30 feet was able, through the medium of a bent wire, to get a spark moving in resonance with the surges of current between the two balls. This was the first oscillator, and proved Clark Maxwell’s theory. Later, a series of Layden jars was connected between’. the two balls, resulting in an improved. oscillator.

TTELEPHONE transmission was at this time becoming rapidly improved, and a Londoner named Hughs became interested in the perfection of the microphone. Hughs discovered that + With his instrument he could at some hundreds of yards detect leakages in telephone lines, and he stated that it would ‘be possible to-develop a new science on these lines. Hughs became quite a familiar figure in his quarter of London, being known as a "rather queer fellow with funny ifeas." He could be seen well into the night moving stealthily along the dark streets, dodging backwards and forwards, holding a strange instrument to his ears. He was intercepting wireless signals. Thus, while Maxwell was predicting wireless telegraphy and Hertz searching for it, Hughs was actually using } it. But in common with so very many other genii, Hughs’s efforts were frustrated and he, very disheartened, turned from his experiments. The attention of Sir Oliver’ Lodge was attracted’ towards this new science,.and he commenced .a series of

experiments specialising in tuning, and it is to him we owe the variable tuning coil. In 1890 Brandly invented the coherer, an instrument more sensitive than any of its time, for detecting the presence of wireless waves. PART from all these movements in Hngland, a young Italian, or should it be said, half-Italian, for this boy TTEPTITTETULTTEANTUITURAEERETUEVEU DIET EOyTRTAT Ora yeRrTOETECPOEVErT NNER ETE erersiereE TTT

was born of an Irish mother, was becoming deeply interested in wireless telegraphy. He had rigged up in his father’s garden, a transmitter and receivcr, and had developed the science along lines of his own.. This was the youth Marconi. His first contribution wa an improved Hertzian oscillator, for he found that by connecting one of the balls to earth, transmission could take place from a considerable distance, By 1896 the science had been developed by Marconi to such an extent that it was able to be used in connection with the illness of Prince Edward (late King) in that bulletins were transmitted from his yacht to Osborne House on the Isle of Wight. In 1899, the first message was transmitted across the Hnglish Channel, and in December, 1901, Marconi essayed to fulfil! his dream-transmission across the Atlantic. With a powerful’ transmitter erected in Oornwall, and a receiving station. in Newfoundland, Marconi and his two friends set. about bridging this great gulf. Conditions were against them, and for three days they ‘listened in Newfoundland without suecess.,

Aerials had been suspended from balloons, and two of these had been swept down by the high gales, but undaunted, Marconi persisted, and at: exactly 11.30 on December 12, the first faint, but distinct signals, 8.0.8., were detected. The Atlantic had been crossed. UP to this time, all the transmissions had been made on interrupted 1

Pedi PLST LHe SE THATAY Att | the grid, and by impressing signals waves, or what is more familiarly known as spark ‘transmission. Series of dots and dashes were all that could be sent, and attention was focused on the sending and receiving of voices, or what is known as continuous wave transmission. The first attempt at this culminated in Pulsen’s singing are, 2 device which, although very inefficient, enabled music and voices to be transmitted for a short distance. The crystal detector was already in use, but there were so far no means of amplifying the signals, , PERHAPS the greatest impetus that any science has received was given when in 1908 Fleming and De Forrest independently discovered the thermionic valve. . Fleming, the Englishman, discovered that if a hot filament and a cold plate were both enclosed in a vacuum tube that signals could be detected. Almost simultaneously De Forrest in America made the same discovery, but introduced-a third element, upon this grid enormous amplification was poasibla. ,

The result of these discoveries is wireless as we know it to-day. The extent to which these discoveries have been. developed are realised by anyone who is at all conversant with. radio literature. When one realises that in New Zealand he can hear amplified to an enormous extent the natural creakings of a wall in Brisbane, he will realise to some extent- the significance of the discovery of these two genii. Wireless now moved forward at an amazing pace. The Armstrong. circuit was probably the most outstanding invention of this period. Armstrong discovered that if the output: of the plate was fed back to the grid coil, enormous amplification could take place within one single valve. This we know as reaction.

‘HD war period, 1914 to 1928, hurried forward the development of wireless telegraphy and telephony. In 1915 the first telephone message was "wirelessed" across the Atlantic, when a man in New York "rang up" another in the Hiffel ‘Tower, Paris. During this period, -the wave-lengths ranged between ten’ and twenty-five thousand metres, or,° as We would say now, between three and .12 kilocycles .per . second. -For'the réception of these frequencies induction coils. of great length were necessary, and*‘visitors to the exhibition will remember the very big coil that was exhibited on "Radio Record" stand. This was a relic of these days. Prior to this, the shorter waves had been used, but = the longer ones were resorted to because of their apparent greater carrying power. Following 1916, experiments were conducted in the use of shorter waves. By 1924 transmission was taking place in ‘the region of'100 metres or 3000 kilocycles. Broadcasting as we understand it today began in 1921 when a few stations were established both in America and on the Continent, and from this date its permanency as a factor in every home became established. From that date, too, its story is known to all. _ The Beam. " N 1924 Marconi became interested in beam transmission. It might be e=.plained here that if a parabolic mir-

ror intercepts parallel rays of light, they will be concentrated at one point, and that the focus. Conversely, if a point of light be situated at this focus the beams will leave the mirror travelling in a parallel. direction. Marconi found that this could be applied to wireless, the reflectors being suspended aerials. The first transmission of this nature took place between London and Birmingham. It was then that its outstanding value was realised. It requir-' ed less power, it was less susceptible to atmospheric conditions, tracts of mountains interfered little with its course, it could be relied on for sixteen hours of the day, it required less power for the same signal strength, and it could be kept relatively secret. _ Following this discovery, a beam service hetween Bngland and Canada was established, and later, between Hngland and Sydney. For a while, it seemed that it would displace cables, but a mérger between the cables and the beam took place this year. Wireless Compass.

ANOTHER important development was that of Tossi and Belini-the wireless compass. This is an application of the principle of the frame antenna,~which will receive signals strongest when pointing in the direction of the transmitting station. In 1916 the value of this compass was evident by an incident in the Battle of Jutland. When the German fleet was moving rapidly towards the English shores, and the Grand Fleet had been called, it was stated that a wireless compass was the means of a final decision for the Grand Fleet to go to the scene of action. A signal was picked up from a German ship 300 miles distant, and an hour and a half later this had varied by 14 degrees, showing that the fleet was moving rapidly towards the English: coast. This has been an invaluable discovery for aeroplanes. A small indicator scarcely larger than a cigarette packet is now installed upon earoplanes flying on certain routes in America and England. Transmitting stations are ar ranged on these routes so that the ‘strongest path of the signals will be along the route to be taken by the aeroplane. Two reeds within this apparatus indicate whether the *plane is moving to one or the other side of this wireless path. The shortening of these, reeds indicates that their destination is being neared. They entirely disap-

pear when over the transmitting station. By this means, an airplane can be on time to the minute when land has not been seen since it left its point of origin. Next week this article will be concluded by an account of the development of picture transmission, radio vision, modern valves, and radio of the future.