The Story of Short Waves

Radio Record, Volume IV, Issue 40, 17 April 1931, Page 1

The Story of Short Waves

by

R. J.

Orbell

B.E.

(ZL I AX)

RAP ENGINEERING, probably more than any other kindred science, has undergone radical changes during the past decade. One of the most outstanding of these undoubtedly has been the development of short wave operation. So far-reaching is the result of this discovery that not only is the olasystem rapidly being discarded in favour of the new for long-distance

communication, but there is opened a vista of future developments which falls little short of staggering the imagination. The whole aspect of radio has been changed. Enormous distances are being covered with almost unbelievable low power, and with apparatus costing only a fraction of the layout required for the earlier long wave transmitting equipment. Just over ten years ago all long-distance radio was catried on in Morse code, on wavelengths varying between.8000 and 23,800 metres, the latter wavelength being that of the great station at Bordeaux, in France, built in 1920, which used a wavelength longer than any other station has ever done for commercial purposes. Enormous power was necessary to force signals through the almost continuous atmospheric interference which exists on ose very long wavelengths. Results were very uncertain as in many localities in the world the stations could be heard well only on rare occasions. The general trend was to longer and longer waves, as it was believed in those days that the longer the wavelength, the better would be the result. {The shortest waves then in use were those around 600

metres, for ship to ship and ship to shore communication. Although this wavelength still holds and is specially suited for this purpose for short distances, recourse to shorter waves for longer distances between ship and shore has taken place recently. Following’ on the ever-growing interest in radio, many experimenters all over the world built apparatus of their

own for purposes of research. This was the case particularly in the United States, where no severe restrictions were placed on amateur experimenters, in contrast to conditions ruling in most other countries. It became necessary, however, to introduce legislation in the United States to prevent interference between amateurs and commercial stations. To this end the amateurs were given all wavelengths below 200 metres for their own use, it being considered that 200 metres was too low to cause any interference with ships or commercial land stations. Incidentally, such ‘"‘low’’ wavelengths were considered useless by the authorities. . All transmissions to date were conducted by the old spark system, with the exception of the high powered commercial stations which used high frequency alternators of the Alexanderson type or of the compensating wave arc system. Both of these latter systems operate more efficiently on extremely long waves. Valves of the de Forest audion type had been used for receiving purposes priot to the war, and improved (Continued on page 29.)):

r he Story of Short-Waves ) {Continued from page 1.)

types were developed in France during the war, but the valve system of transmission was used only to a very limited extent by experimenters till about 1922, About this time development was rapid. Amateurs in the United States conversed from: coast to coast using 200 metres and below with much lower power and with much greater freedom from interference than did the commercial stations. Signals from American amateurs were being heard in New Zealand, the first New Zealander to receive definitely an American ama teuw being Mr. Ralph Slade, who then resided in Timaru. The 200 metre signals from 6KA were heard by him and confirmed by letter from Los Angeles. Other American stations were heard in large numbers by Mr. Frank Bell at his station at Palmerston North, as well as by the writer in Christchurch. The double honour of being the first to hold two-way communication with the United States, and also with England, went to Mr. Bell, the latter achievement taking place on October 18, 1924, _. This same day the writer arrived in England with an experimental shortwave transmitter on board s.s. Port Curtis, from which. ship two-way communications with Mr. Bell, Mr. Ivan O’Meara, of Gisborne, and other New Zealanders had been conducted during \ the voyage.

It was with a strange feeling that the writer went to the station of Mr. Cecil Goyder, G28Z, in London, with which Mr. Bell had been in communication, and on the following morning, when Mr. Goyder again got in touch, spoke back and forth to Mr. Bell in New Zealand with as much ease as if we had been but a short distance apart, This, and all other communications at this time, were conducted in morse code on wavelengths of from 80 to 100 metres. Later, telephony was first transmitted successfully to New Zeae land from England by Mr. Gerald Marcuse G2NM, of Caterham in Surrey. International communication between amateurs rapidly became an everyday occurrence as the lower wavelengths of 40, 30 and 20 metres were used. Interest by Commercial Stations. {= was natural that the attention of commercial interests should be directed to the use of short waves, both for morse communication and for broadeasting over -great distances. Many of the larger longwave broadcasting stations in the United States and Europe built experimental shortwave broadcast transmitters, conspicuous among which are the British Broadcasting Corporation’s station . at _ Chelmsford, 20 miles from London, This plant, which uses the call sign G5SW, conducts regularly daily 25metre transmissions, which dare readily heard in New Zealand by owners of shortwave receivers. G5SW_ relays the programme broadcast by 2L0O, London, as well as "Simultaneous" programmes to the other stations trans: mitted from any one centre in the British Isles. . Special events of inter-.

est such as boat races, cricket and Rugby fixtures, special services in St. Paul’s or Westminster Abbey, etc., are always broadcast by G5SSW specially for reception in the Dominions. © Other European stations have: their shortwave transmitters, including the Vatican station in Rome (call sign HVJ), which has recently commenced regular transmissions.’ This latter is one of the highest-powered shortwave te eee | team Ot 08

stations in the world, utilising 50 kilowatts, which, if necessary, can be stepped up to 100 kilowatts. POJ, in Holland, transmits programmes regularly for Australia and New Zealand. In the United States, the American General Electric Company’s shortwave stations are heard with great clarity in New Zealand practically every afternoon. "There are many other United States and Canadian broadcasting companies which have realised the possibilities of short waves and have developed their own shortwave equipment. Even Japan, French Indo-China and Russia have all installed high-powered shortwave stations which are received in New Zealand with great volume, In fact, there is: an ever-increasing number of stations too numerous to mention, in all parts of the world, which have installed, or are installing, similar equipment. ; _ Modern Shortwave Receivers. WHils shortwave stations have been increasing in’ numbers and effi-~ ciency, developments in receiving apparatus have also been taking place. The advent of the screen-grid valve has rendered possible much greater amplification of the received signal. While the three ‘electrode valve had been suitable for use with long waves It became quite uncontroliable when attempts were made to:use it for amplifying . shortwave -radio frequencies. ' -Experimenters: found, however, that the new valve provided not only a satisfactory ‘solution, but the amplification rose till it was practically equal to that obtainable from powerful longwave apparatus. Hitherto the tuning-in. of shortwave stations had been somewhat difficult ---eS ra eee AE PPT, cake! gs ea | :

owing to the weak nature of the signal received, whereas two. stages of screen grid amplification provides a signal of .such intensity as to render the tuningin of short waves 2 matter of. extreme simplicity. «Owing to the very high frequencies involved, however, great care in receiver design is. essential: if the: full amplification from two radio frequency stages is to be obtained. Gertain factors in the design of shielding for instance, which are unimporiant in longwave receivers, become essential when such high shortwave amplification is involved, ; The best of apparatus should be utilised throughout, as nothing tends to ruin results more than condensers of poor quality and poor insulation generally, when high frequencies are involved. The modern receiver should be capable of the reception of both long and short waves at maximum efficiency. This is the ideal combination and one that is becoming more and more in demand as the utilisation of short waves becomes more and more general. There are receivers on the market in New YVealand at the present time which fulfil both these requirements to a degree bithérto unobtainable. Latest circuit developments have done away with any sacrifice of efficiency on Jong waves in order that short waves should be.received. In fact, greatly improved results on both wave bands are to be had. The time is arriving when the purchaser of a radio set will demand that his receiyer should operate on all waves, He will realise that unless this is the case he is missing much of the radio entertainment available to him. The range of his set without ‘short waves is cramped to a radius of a thousand miles or so instead of the whole world. Stations May. be Heard in Daylight. NLIKB long waves, short waves are capable of travelling great distances during daylight hours. The shorter the wavelength the more does this become true. Thus wavelengths of about 80 metres will provide good reception all over New Zealand in broad daylight, when long waves are unsatisfactory. Except when high power is used, however, the limit of the daylight range for 80 metres is about 800 miles, unless unusually good conditions exist. This refers to daylight at both ends.

_If one end ig in darkness, the range is increased considerably, -On the other hand, wavelengths, jn the neighbourhood of. 40 metres have an average daylight range. of from 3000 to 4000 miles, whereas wavelengths below this: value have a correspondingly greater range by day. The ‘fact is noticeable when listening in New Zealand for United States short wave statlons on late afternoons. ‘The first stations picked up are those operating on the lower wave barids, about 30 metres or below. Those operating on about 50 metres do not come through with great Strength till evening approaches. The reason for this is that during our afternoon in New Zealand the twilight band is sweeping gradually across the Pacific Ocean, so that the amount of darkness between New Zealand and the United States increases till finally there is darkness all the way between ourselves and the American station. As a matter of interest, it has been ascertained quite recently. that wavelengths below 10 metres. will not travel more than a few miles in darkness, although when there is daylight at. both ends, the range often-is thousands of ‘Tiles. The use of ‘these very short waves, however, has several disadvantages for purposes of broadcasting, which as yet have not been surmounted, although a recent cable from London indicates that some Frenchmen have perfected a system of telephony which operates on ultra-short waves. Seasonal Effects. (GG ENDRALLY speaking, although the change of season from summer to winter and vice versa affects short wave reception only in as much as it constitutes a change in the daylight conditions, there are several points in connection with seasonal effects which should prove of interest to owners of short wave receivers. For instance, the best time of day for reception from Hurope changes very markedly with the season. During the winter months, from March till August or September, station G5SW in England may be heard in New Zealand strongly during daylight hours from ahout 6 am. till noon, but about midnight, reception from this station: generally is not so clear. On the other hand, during our summer, reception conditions are reversed, GSSW being heard more clearly about midnight than at the above times. This effect refers not only

a to GBSW, but also to other northern’ European stations, such as POJ in Holland.. Reception from stations situated in the south of Hurope, such as 8RO, Rome, are affected less than those in the north. The reason for this seasonal -effect is made apparent by reference to 2 globe of the world. During New Zealand’s winter, the earth is tilted at an angle with respect to the sun such that the shortest path in greatest darkness between England and New Zealand occurs during our daylight on a great circle running south from England. During our summer, however, it will be seen by referring to the globe that the shortest path in greatest darkness

is during our night on a great circle running north from England. As the average shortwave length prefers darkness, although travelling in daylight also, as explained previously, the best times as regards day and night for reception from England and Europe generally are as stated above. Reception from these places duri .g twilight hours generally is at a peak, independent of the season, for then darkness covers almost the entire distance for a short period. Antipodal Effects-Ideal Position of New Zealand. OWING to the fact that our earth is spproximately a -sphere, and also to the fact that New Zealand is very close to being situated at an opposite or antipodal position from England and Western Hurope, there is quite a marked concentration in and about New Zealand of waves transmitted from stations in these places. This means that European signals are heard here with greater strength and clarity than is the case in countries considerably closer to Europe. Proof of this concentration effect at opposite points on the earth is had in. several cases. For instance, Hawaii is one of the best places in-the world for reception from South Africa, these be- ing places situated at almost antipodal points on the earth. From the point of view of shortwave radio, then, New Zealand is in the fortunate position of being situated as far as possible from BHurope, resulting in improved reception here. There are other reasons why New Zealand is for.

tunate in this respect, one of which } being its insular position. The less land that radio waves, both long and/ short, have to travel over the less absorption takes place during their passage. This absorption is due.to irregularities in the Heaviside layer existing over large land masses and continents. Experiences in the Antaretic. DvRine three months of last year, when the writer was connected with the shortwave radio equipment of the Byrd Antarctic Expedition, some very interesting experiences were encountered. Although radio behaves very much as usual in the Antarctic, there are. a number of instances when it does not do so. While travelling to the Bay of Whales, the City of New York, the.supply ship, passed south and to the eastward of the South Magnetic Pole, where strange fading effects were noticed. During this petjod, there was no darkness and no night, as it was summer time, although during night time in New Zealand, darkness or twilight existed to the north of our position. , Just to the north of the Magnetic Pole reception on long waves from New Zealand was extremely good on one "evening" in particular. 2YA, Wellington, was received at great strength, and was quite as loud as it would be in most parts of New Zealand. However, 24 hours later the ship had passed the latitude of the Magnetic Pole, . and 2YA, as well as all the other New Zealand stations, were quite impossible to receive, All that could be heard of 2YA was a very weak carrier wave. A similar effect was noticed on another occasion when the Japanese stations were heard at abnormal strength, . and 24 hours later were ‘not audible. Results with shortwaves were very er-/ ratie at this same period. Shortwave telephony was accompanied by very rapid fading, as many as ten fading periods in one second being noticed, giving an amusing though peculiar shivering effect as though the signals were affected by the low temperature prevailing. During these times it was almost impossible to read shortwave morse signals owing to their broken nature. _. When: the City of New York approached the Bay of Whales reception returned to normal, excellent results being obtained. The all-wave receiver used during these experiments was one of a well-known local make which gave splendid results. These phenomena point to the probability of reflection and screening of short and long’ wave signals in the neighbourhood ot./the Magnetic Pole. They also indicate the probable reason why shortwave signals do not pass freely over either the North or South Magnetic Pole as is instanced by poor reception in New Zealand from South Africa and vice versa, and between England and Alaska, where similar poor results are obtained. Probably auroral effects are largely responsible for these results. Incidentally, this Expedition provided but another example of the ever-growing uses to which shortwave radio may be put. Without it the Expedition would have been cut off from the rest of the world, as were the Shackleton and Scott Expeditions before the days of radio; whereas, with it, not only was every movement of the Expedition known immediately in New York, but the members were able to hear actually the voices of their relatives speaking distinctly to them from America, 10,000 miles away, and were able to send reDliest