RADIO AND ITS RECEIVERS

Sun (Auckland), Volume 1, Issue 19, 13 April 1927, Page 12

RADIO AND ITS RECEIVERS

AERIALS—No. 1. By “RAYTHEON.” If one were to take a walk through Seme of the residential streets of the city and suburbs, it would be an object lesson on how not to erect an aerial. The antennae used for broad-cast-receiving work will be found to be many and varied. Some will show a thoroughness in construction and design which is to be highly commended. On the other hand the majority will prove to be very haphazard, makeshift affairs. Where permanency is assured for the receiving set, the erection of a simple, yet efficient aerial, is paramount. It is not only unfair to yourself, but the set and the dealer who supplied you. to use a mediocre antenna. Accordingly these few lines it is hoped will prove of assistance to the. beginner, and those others who should now be overhauling their aerial system, as the winter season is fast approaching, when better conditions should prevail, during the usual periodical examination. FIRST CONSIDERATIONS The particular space and surroundings of the site govern the erection of the aerial. A large section naturally provides a good location if there are no large metallic structures immediately nearby. Where the location is congested quite a good deal of judgment will have to be exercised to obtain the best position available. The reason for the erection of the aerial is to collect the radio-frequency energy that is radiated from the broadcasting stations. As most are probably aware the actual amount of this energy collected by the receiving antenna is exceedingly small; in fact, so small that only the most sensitive devices can measure it. A small aerial will in consequence pick up relatively less energy, while should the length of the aerial be increased, the receiver will tune very broadly. Consequently we must arrive at a happy medium. Probably for the best allround results, a single wire (solid, stranded, braided or ribbon), measuring about 60 feet in the horizontal portion, 40 feet for the lead-in (to the terminal), and not more than 20 feet for a ground connection, will best serve. As regards the kind and size of wire used, this depends mainly on one’s own preference, though in some instances one form will prove more satis factory than another. Bare copper wire, solid or stranded, will be best for an aerial where the location is reasonably free from smoke, soot and excesive dust, providing it is not close to the sea coast, or in a region of thermal activity. In these latter locations, and also close to the city, the enamel-covered aerial wire is recommended. Stranded wire being more flexible than the solid, it has a slightly greater mechanical strength, and is also a little better in conductivity over the equivalent size of solid wire. As regards electrical efficiency, the size of wire does not matter a great deal, but there is a decided difference in mechanical strength. Seven-twenty stranded wire has roughly twice the tensile strength of 7/22, but of course is also much dearer. Again owing to the Fire Underwriters’ Regulations, which require nothing less than No. 14 or its equivalent as lead-in wire from the aerial, it may be better and more convenient to use 7/20. If a straight-line aerial or inverted “L” type is used, the wire can then be used in one unbroken length. AERIAL MATERIAL NECESSARY Before commencing to erect the aerial the builder will be well advised to assemble all the parts required before commencing the construction. Hereunder is a complete list of parts which comply with the underwriters’ regulations. 1 coil aerial wire, 100 ft. 1 coil lead-in wire (see later note). 2 insulators (glazed porcelain, glass, or pyrex). 2 or 3 knob insulators (porcelain or glass stand-off insulators). 1 lightning arrester (outdoor or indoor). 1 lead-in terminal or strip. 2 ground clamps. 1 coil 50ft. 1/14 or 7/21J cable insulated. 1 box insulated staples. 1 roll friction tape. Solder and solder paste (latter not required if resin-core solder used). If a mast has to be erected do not forget the required amount of galvanised guy wire, rope halyard, pulleys, etc. INSTALLATION EFFICIENCY POINTS Bear the following points in mind for a highly efficient aerial: 1. —Over-all length not to exceed 125 ft., from free end of aerial to antenna binding post on set. 2. —No close approach to trees or buildings. 3. —Horizontal portion as high as possible. 4. —Lead-in away from building. 5. —Absence of joints, where possible. 6. —As few insulators as possible. 7. —Ground wire to be connected to good earth. 8. —Set not far from where lead-in enters house. 9. —Wire fairly heavy and rigid. 10. —Clean connections throughout. 11. —Straight well-secured masts. The most efficient aerial is of the outside type, placed as high as possible so that it does not come near or in contact with trees and other obstructions. (Part 2 of this article next week.)

OSCILLATING RECEIVERS Despite the fact that much has been written and a good deal broadcast, on the above subject, the nuisance is still very prevalent judging by the writer’s experience last week. It would seem that in the majority of cases this is due to novices who persist in trying to receive distant stations beyond the capabilities of the set they are operating. Why an owner with such a set will persist in his attempt on one station for half-an-hour or more, when success is quite obviously impossible, beats one’s understanding. He is not obtaining pure speech or music and most decidedly is preventing others with better class sets from doing so. We are all fully aware that some nights are better than others for reception, consequently, a set that may just receive respectable signals one night will fail to do so on another night. The operator caK soon tell if he is likely to fail, or have considerable trouble, in clearly receiving a given station. If, after the initial signal is located in the tuning of the set, a few seconds adjustment fails to “ clear-up ” the signal from the station, it is wiser to make no further attempt. Not only are you spoiling the reception and entertainment of other listeners, but which to you as owner should be more important, the set is being strained or overworked. This means that with constant usage of this nature breakdowns will occur in transformers, condensers, etc., that in the ordinary course should not happen. Again, and probably of still greater interest to the owner, the valves will rapidly lose their sensitivity and “ B ” batteries deteriorate. Under these circumstances consider your set, and the other fellow, and if in a few seconds you are not able to clear up that signal, desist,

and save your fellow-listeners from th. sin of profanity, at least. TYPES OF SETS Herewith is a brief summary of th. chief types of radio sets. No trade names are given for the dealer can in form you as to the type of circuit used in any set he may have. SIMPLE DETECTOR CIRCUIT The simple detector circuit is free of distortion, but is naturallv not as selective or as powerful as some others REGENERATIVE CIRCUIT So called because it feeds back into the valve electrical energy which has already passed through it. The cir cuit is fairly selective and also gives reasonable power, under ordinary favourable conditions, having a raneV of from 500 to SOO miles. However because bf its oscillation, or squealing’ especially when tuning, there is often quite a lot of distortion. The regenerative set through being such an easv oscillator, thereby becoming a small transmitter, very often causes trouble to others listening-in. Its main advantage is its inexpensiveness. UNTUNED RADIO FREQUENCY This circuit employs two amplifying valves, usualy two, so that very weak signals are built up in strength before they reach the detector. As a rule there are also two audio amplifying valves to build up the volume after the signal has been passed in by the detector valve. Naturally this type of set has the ability to receive signals which a detector alone would not get. However, one drawback of this circuit is that it does not do justice to ail wavelengths. THE REFLEX CIRCUITS With the reasonably-priced valves of to-day there is really little call for this class of circuit. Reflex circuits were originally brought out to save expense in the number of valves used. In these circuits all valves except the detector valve are employed for both radio and audio frequency amplification. The drawback is, that although the valves will do the work, they are practically overloaded all the time. THE SUPERHETERODYNE This was designed to convert ordinary broadcasting wave-lengths to much longer wave-lengths, for the simple reason that radio frequency valves operate better on a longer wavelength. It is rather complicated in construction and fairly costly to build. Usually eight valves are employed in the circuit and sometimes more, sometimes only six. TUNED RADIO FREQUENCY Tuned radio frequency does all that untuned radio frequency does and more. It can be tuned to the wavelength you want to the exclusion of others. The one trouble, however, is that it often oscillates like a regenerative set. THE NEUTRODYNE This is really a variation of the tuned radio circuit, but has the distinct advantage that it is designed to “ neutralise ” or eliminate the oscillation sounds. Probably for all-round purposes the neutrodyne is one of the most satisfactory sets. It is selective, gives excellent tone, and has quite a considerable distance range. One of its great advantages is the ease in tuning. Another advantage also is that the same station always comes in on the same dial settings..