FEEBLE RADIO CURRENT

Radio Record, Volume I, Issue 13, 14 October 1927, Page 15

FEEBLE RADIO CURRENT

TO AVOID LEAKAGES SOME GOOD POINTS. Even in a set which has been built of the best materials, which has been constructed by the best of radio engineers and which operates ‘perfectly" the percentage of the initial electrical impulse which has been utilised is very small. That is to say, the efficiency of a well-constructed and well-designed receiver is far from being 10 per cent. There are vertain factors in energy losses which man has not been able to overcome. Some of these difficulties have been dealt with to a certain extent successfully. | Careful Insulation. It is in the aerial and earth systems that the first losses of the received cnergy are sustained. The aerial should present a large surface of bare metal. Serious leaks are to be found in faulty insulators or insulators of poor quality. For alkround satisfaction employ the finted or petticoated glazed porcelain insulators. ‘These will generally be found to hold up in all weather and under. severe physical strains. Bring your lead-in through a window pane. If this is not possible insulate it with a porcelain tube. An immense loss will result from jamming the lead-in under a win- @ dow, not to speak of the danger incurred. Keep the wire away from the building a foot or more if possible to prevent absorption of the received waves. ‘The earth system has one main danger to be guarded agaiust, providiny that a good earth has already been. established. Be careful to keep high resistance joints out of the cirenit. This maxim holds for the aerial and the wiring of the whole set. Sources of Losses, | Among those losses over which man. has little control are those resulting. from difference of electromotive force of two parts of a circuit. This has yenerally been known in the case of a wire-. wound inductance as distributed capacity loss. It is on account of this loss: the bank-wound coils are wound in a. particular manner and not layer upon layer. Another source of trouble is poor insulation. Shis difficulty has been come to a very great extent, but in dea:- | ing with electrical impulses at radiofrequency the problem of insulation must be carefully regarded. In the true sense there is no substance that has yet been found which has perfect insulat- itig qualities. An insulating material is one which offers a_ resistance high enough to retard to a great extent the flow of electricity. China and glass may both be called insulators. They differ only in degree of insulating properties. There is no well defined line between fusulators and conductors, because each as to some extent the properties of the other. In a general wav all metals are good conductors, and glass, porcelain and rubber constitute good insulators Avoid Resistance. Aside from such uncontrollable (to some degree) energy losses, there are mmany ways. in which energy is lost that are inexcusable. When constructing a set keep in mind that the initial impulse is very feeble, wire and arrange your set so as to offer as little resistance to it as possible. It is a known fact that electricity travels on the surface of its conductor. Never use a wire of small diameter for connection between instruments when a wire of fairly large diameter is available. No. 16 aerial wire is a good wire for wiring a set, although proper ‘"‘bus" wire is better. Bare Wires Best. Because of absorption, another of radio’s seemingly insurmountable difficulties, bare wire should be used whereever possible. Wire insulated, first with a single laver of cotton and then one of silk, is very efficient and very neat appearing in coils. In wiring the set, if a rather intricate job is encountered, and "‘bus’" wire is not available, use heavy copper aerial wire and cover ¢his with natural-coloured varnished cambric tubing or "spaghetti.’? Always nse insulators in their natural colours if possible. Some of the dyes that are employed in colouring them have strong powers of absorption or conduction orboth. Advice On Wiring. Every wire in which an electric current is flowing has about it a magnetic field. It is this property of an electric current that is taken advantage of in couplers and transformers of all kinds. The field of a coil is much stronger than that about a single wire. This property, although most useful and eéssential in our receivers, constitutes a source of tronble alone. Never run high-frequency wires parallel to each other if they are within an inch and a half of one another. The field abont one or two parallel conductors may set np a current in the wrong direction in the other, This last is called an induced current, for it is set up by the induction of another current. If the induced current "bucks" against the current already flowing in the wire it can readily , be seen that trouble will result In circuits employing a tickler coil for regeneration, care must be taken in placing the coil in position so that its windings are in the same direction as those of the secondary, Otherwise the fields of the two coils will counteract and neutralise each other. Induced Currents. While we are speaking of induction ’ % would be well to caution against trowding the parts of a receiver into too small a space. Amplifying translormters are surrounded by, a strong

magnetic field, and for this reason should be as far removed from the tuning units as possible,’ Shielding these transformers with a metal case helps greatly to dampen this field, but does not prevent some of the strongest lines of force from breaking through. In some cases action in the radio valves: is paralysed on account of some-strong magnetic field in their proximity. Proof of this statement can easily be had by the experimenter. Set your outfit. into operation and then place a large horseshoe magnet around your valve. Swing the magnet around in a circle in a horizontal plane and ‘notice the effect produced on the signal strength Avoid Dust. A common factor which lessens the efficiency of a’ set is dust. Dust causes leaks of high resistance all over the set. A heavy coat of dust will destroy the efficacy of an insulator. If dust is allowed to accumulate on the plates of a variable air condenser, the capacitance value of the latter will fluctuate’ and eause trouble. Wgist must absolutely be kept off the grid leak. | Can you open up vour set and disclose | a shining and neatly-wired’ apparatus ? | Square corners in the wiring helps the general appearance. A _ neatly-and | cleanly-wired set will be found to give | greater satisfaction than one in. which the wiring is a maze of twisted and coil- | ed wires, going to. and coming from | only the constructor himself (perhaps) , knows where. If ever you wire a set as" an experiment, it will pay to use flex-. ihle insulated wire temporarily, and as soon as the set is found to function Lsatisfactory replace with permanent heavy wire.