RADIO NOTES

Dominion, Volume 23, Issue 218, 11 June 1930, Page 16

RADIO NOTES

By

“ETHER”

Placing of Aerials. A. reader has sent in a query regarding danger from' power lines situated close to aerials. Considering there is scarcely a single town of any size in this country without its web of power lines the subject is of sufficient importance to interest nearly every user' of radio sets. "Cautious,” in. his letter, says: “The Public Works Department propose to build its main transmission line (110,000 volts, I think) through some property in which I am interested in Taranaki. The line passes within two or three chains of the house in which a wireless set is installed, and within one chain of one end of the aerial.” "Cautious” raises the question as to the safest and the best all-round position for the aerial. His aerial as at present erected is almost at right angles to the power line concerned. In the first place, where high voltages in the nature of that mentioned are under consideration, a shock is instantly fatal. For this reason it is wise to place the aerial as far away from the line as it is possible to do. Power Line Dangers.

For instance, if a lofty aerial mast were erected near a power line carrying 110,000 volts, and one of the stay wires broke loose and touched the line, the small egg insulators and probably the usual aerial insulators would not be any obstacle to the whole of the aerial and guy wires becoming dangerously alive. If nobody happened to be near the set possibly all that would happen would be that the set, its aerial, and other incidentals nearby, would melt or crumple up or catch on fire. Obviously a new receiver would be indicated afterwards, perhaps a new house. If part of the aerial system made alive in this manner made contact with gutterings or other metallic parts of the house, most of the metal work, including, of course, the roof itself, would become alive, and anyone touching it would be killed instantly. Under the circumstances it would be only wise to erect the aerial mast at such a distance from the' power-line so that in the event of anything coming loose or falling down it could not reach ■ the power-line. A distance of one chain is rather fine if a high mast is used. However, there are other reasons why it is wise to keep the aerial as far. away from a line as possible. Interference from high voltage power-lines diminishes greatly for every few feet extra that, the aerial is separated from them. Interference. ,

At a distance of over a hundred yards interference,- although it- may not be negligible, is probably tolerable. From a geometrical point of view the best way to keep the aerial as far. away from a powerline is to place it parallel to it. Unfortunately this is where Mr. Euclid and radio disagree. An aerial placed, parallel to a power-line is precisely situated so that it picks up the very maximum of interference from the line in question. For this reason it is good practice to place an aerial at right angles to any source of interference such as a powerline. In the case of “Cautious," who provides a rough diagram, the power-line passes the house on a slant The best place for the aerial,, if it is possible, is where the.slant is widest. If possible it would be best to move that mast from its present site one chain from the line and replant it as near the house as possible. This might make a “T” aerial inevitable. The down-lead would then come from the exact centre of the. horizontal portion of .the aerial rather than from one end. There are no objections to “T” aerials at nil. In fact in many cases they are superior to the ordinary “L” type. As regards details of power-line interference and how they occur, the matter was treated fairly completely in last week’s notes. Unfortunately high voltage lines of this nature are very difficult to keep quiet from a radio point of view. However, the Public Works Department say that their-high voltage lines, owing to the use of suspension insulators and clamps in place of binding wires, are very silent. So far there have been no complaints of interference, they declare, from their 110,000 volt lines. Soldering.

In spite of patent terminals and other aids to radio enthusiasts who are not yet very expert on the job, the gentle art of soldering forces its way upon them at a very early period. A soldered joint is as permanent as the Pyramids of Egypt if properly done. A clamped joint is as unreliable as party politics. It falls to bits with age, and is at the mercy of the outsidc.tarld. Any dumped joint over two years old should be treated with suspicion. Thin layer of oxidisation creeps in, and does its best to make the joint into a not very efficient metal rectifier. Yet one can see people who have gone to all manner of trouble to dodge a little ■ bit of soldering that would have taken them but two short minutes. Speaking generally, the entire wiring of a set should be .soldered where one wire makes connection with another. For neat work all wires to terminals should be soldered at the end of their shanks furthest from the panel; furthermore, it is better to solder a terminal tag to a wire rather than clamp down the wire direct. Heating the Iron.

The whole art of soldering depends on using the iron at the correct heat. Electric soldering irons are designed to attain that heat, and are delightful to use for that reason. An iron heated extern nally will generally show a curious greenish flame when hot enough. If held near the cheek it will be found to be almost unpleasantly hot. Over-heating the iron results in burning the solder on it, under-heating results in the solder not running. Incidentally in this respect if one part is large and the other, say. a wire," is small, it is no use heating the wire with the iron to the correct heat if the larger object is not already hot enough to run solder. Fluxes.

Soldering consists in fixing objects together by means of solder which at a certain 'heat runs like a liquid, and when cool solidifies into a binding medium. Owing to oxidisation it is imperative'to use some sort of flux, for the two metal parts that are to be soldered must be made bright and clean, and kept clean during the heating process. There are numerous patent fluxes on the market. For radio purposes never use killed spirits, as it has a corrosive action on wires. When soldering a wire on to a terminal shank, heat the shank first and leave a blob of solder on it. Give this blob a shrewd tap with something to see it is really fast. Then put the soldering iron on the wire and press the lot on to the blob. Suddenly the solder on the terminal shank will go soft, and the wire will sink into it. _ The job is done. When joining two wires together either bend one over the other • and solder it, or run them both together for half an inch, uniting them with solder from a properly tinned iron. Tinning.

Tinning the iron is perfectly simple. All that has to be done is to clean the iron when it is hot. A file will do this job Dab it into the flux and then wipe it over with a stick of solder. A clean rag quickly wiped over a hot iron, will generally clean off any burnt particles, and save unnecessary tinning. An iron that looks all black, and to which solder will not adhere, or run. is an iron that requires tinning «R<i>n. Nobody would dream of playing Rugby with a deflated ball, and trying to solder with a dirty iron is even more waste or time. An adept at soldering can connect up a dozen terminals with soldered joints while another person is screwing up one terminal with a clamped connection. Furthermore, breaking a soldered joint requires the application of a hot iron for a fraction of a second, and the job is done. It is very quick. After soldering go roupd your terminal npts with a spanner, for in the case of ebonite the Jwat tends to Jooseu the nu*®.

The Lite of Valves. . Provided a modern valve is not overrun there is no reason why it should not give good service for several years. There is however, a definite limit to the life of a valve. At one time this was measured bv the time it took for the filament to burn out. In these days of valves winch take extraordinary low filament current the life of a valve depends on the emission properties of the filament. These generally fail before the filament itself. As the emission fails the anode current drops, the A.C. resistance of the valve increases and it becomes more and more inefficient, requiring more and more reaction. Power valves are generally the worst offenders, but high frequency valves seem able to go on at the job year after tcst your . valves yourself once a year or to get some reliable radio, service station to do so for vou In many eases valves are still in use’after two or even three years of life The life, of course, is not measured by years but by the time the set is used. A valve not in use will last a lifetime. A valve with the wrong grid bias or too hi-h a filament voltage will last no longer than a few hours’ running time. Take care of your valves and the rest of the set will take care of itself.

Broadcasting the Test Matches. The five cricket test matches between Australia and England played in England are to be broadcast by 2UW, Sydney. This station works on a wavelength of 267, and may he picked up sometimes in New Zealand by sensitive sets. The first match will take place from June 13 onwards, and the others on June 27, July 11, July 25, and the final match at the Oval will take place on August 16. The times of play in England made it possible for 2UW to broadcast the games from 10.30 p.m., N.Z time, onwards. It is hoped to carry out a rather ambitious scheme from this station whereby every hall in every oyer will be described. Before hand details of the wicket, the toss, the weather, and other facts will be given from 2UW half an hour or so before play begins.

Radio Research in Britain. The report issued by the Radio Researeh Board of the British Department of Scientific and Industrial Research covers the work accomplished since the establishment of the board in 1920 up to March 31, 1929, and demonstrates in a remarkable manner the progress of what may be termed the refinements of wireless during the past ten years. It is interesting to note how often investigations which started on what appeared to be purely academical problems have led to results of great service in commercial and practical working. For example, ‘ experiments undertaken primarily to prove the existence of the Heaviside Layer and its miture have furnished invaluable data concerning the phenomena of fading and the choice of suitable wave-lengths for different ranges. The study of the nature and origin of atmospherics involved the use of a special cathode ray oscillograph, from which has been evolved a direct-reading visual direction-finder for ordinary wireless signals which is likely to prove a valuable aid to mariners. The growing necessity for the accurate maintenance of frequencies has especially turned the attention of the board towards the study of quartz resonators and oscillators, and to the construction of standard wave-metres. The difficulties often experienced, especially in rough weather, in obtaining accurate bearings by means of directionfinding sets installed on board ships have led to the further development of the rotating radio beacon, which enables bearings to be obtained with an ordinary receiver and a stop-watch. Among the miscellaneous researches undertaken by the board may be noted the design of a high vacuum pump for use with large transmitting valves in which metal is used in place of glass for more readily dissipating heat. Static and the Parish Pump.

Although the village of Aughnacloy, Tyrone, is far from the madding crowd, it is not far enough from the radio interference which is set up by the electric pump supplying water to the local reservoir. The twenty wireless license holders of Aughnacloy have accordingly petitioned the authorities to stop the pump at 6 o’clock every evening.