A Corner for Beginners

Radio Record, Volume II, Issue 11, 9 November 1928, Page 11

A Corner for Beginners

By

Observer

Faulty Leads. ALKING of aerial leads reminds one _ of an incident told of an owner "who sought to criticise an experienced man before he had thought of what his trouble might be. | An amplifier had been installed to a eryétal set and. the whole outfit left working satisfactorily. Shortly after the owner came in with a "grouse’the set was a failure, it had been examined by an expert and was one mass of faults. : After the annoyed owner had calmed down, it was learned that signals could be heard only intermittently and were then very weak. The set had to be put right or removed. It was put right quicker than the owner had hoped for. To improve appearances, certainly not for any other purposes, a speaker cord had been employed to bring the ground and aerial connections to the set. ‘The trouble seeker. suspecting this, eonnected the set and these terminals by plain wire and without a hitch the set went "better than it had ever gone before." | | Cheap cord had heen used; the insulators being poor had broken down, and had caused a short circuit with the adjacent ground wire. The casual reader may think he has a good idea when it was mentioned that speaker cord was used for leads, but this is unwise. Impulses pass along the aerial wire at very high frequency. and unless the wires are well insulated trouble is bound to arise, When applied to the speaker, the current is less likely to break down- insulation, for it is at low frequency. Incidentally long connections should ‘not be necessary to join the set to the aerial and earth terminals. For the best results these wires should be kept aegis short as possible. .

Symbols. OME time ago a request was made that we publish the symbols commonly used in radio. As endeavours now -are being made to standardise radio technicology and symbols, there is a: Hikelihood of these being altered "hefore very long, so that the list is being withheld for the time being. A Cause of Distortion. {[t often happens that bad distortion occurs which cannot be attributed to faulty batteries, incorrectly biased valves, or valves wrongly placed. It is then that the condensers, especially the fixed condensers that set designers recommend, be placed between transformer and grid, or between plate. of one valve, and grid of the next, should be. examined. After long use, or by eareless treatment, these may break down and allow: leakage, giving distortion. . A simple test which can be applied to ariy condenser can be conducted by following these few simple instructions. Connect one pole of battery to one lug on the condenser. Connect the other batterv terminal to one terminal of a

pair of phones. Now place the t)t\ terminal of the phones on the free lug off ine, condenser. A’ healthy click shfad be heard in the phones. Dischirge the condenser by connecting the lugs, and repeat the experiment. Each time there should be one clear click, and. no more. A series of clicks indicates that the condenser is faulty, and spemust be replaced. | + Noise from Speaker. [= may be that on connecting up the speaker there is heard a loud, purring: noise, which forms an objectional

background. .Atmospherics, which are usually blamed for all these unwanted trouble is in the batteries, for runthis case, Naturally the first place to look for trouble is in the batteries, for rundown batteries can cause a multitude of troubles. Failing this the next most likely cause is a faulty grid leak or 2 broken connection to the grid terminal of the detector valve. Faulty grid leaks may cause many troubles even to giving the set a harsh tone and

it is well to keep spare parts on hand. Some eliminators give a purring noise, known as motor-boating, as the sound resembles the exhaust of a motor boat. Another unwanted noise may be caused through the elements of the valve vibrating, resulting in a loud pang." The valves it would be found vibrate easily and sometimes a heavy footfall may be enongh to set the elements moving resulting in this disagreeable noise. On being started this may continue several seconds, gradually dying away. The trouble is seldom apparent in sets constructed by experts, but quite a feature of those home made. It iss easily remedied by the use of shock absorbing sockets, in place of the ordinary fixed type. ACH time the loud speaker or phones are plugged in a distinct click should be heard. If this is not heard; all "B" battery connections and plate leads should be examined. Sometimes the plug itself becomes faulty.

Aerial and Earth Troubles, ROUBLE arising from faults in the aerial-earth systems are often difficult to locate and may seriously impair reception. ~The easiest way out of this difficulty is to erect an efficient aerial, for the more efficient the aerial the. cheaper and easier to maintain the set. ‘The aerial collects energy from the, ether and it is obvious that its efficient collection. must be a matter of great importance. . It is:a common mistake to believe that any sort of wire put up anyway will do for an aerial. Because signals

are received from such an aerial, it is not to say that the listener is getting the best results, and none but the best are worth while. . No wireless engineer would think of using anything but high conductivity wire-that is wire that permits of the easy flow of electrical impulses, for his aerial, . A point even more neglected is to have a good earth. It is a prevalent idea that any piece of old wire, no matter what its dimensions may be, will do for an earth lead, and any rusty kerosene tin for an earth, Again it is boasted that good reception may be obtained but that is beside the point. By the substitution of a better aerial or earth, improved reception is assured. The earth lead should be short, and wire at least as heavy as the aerial should be used. The idea is to give the least resistance to the return flow of the current. Diseard that long jointed piece of wire used for an earth lead and substitute 2 short stranded cable. The result will surely be worth while. | Joints, OO much cannot be said about joints for almost every would-be listener, on arranging his aerial-earth system, not knowing nor worrying about principles of electricity, neglects to clean the joints. Reference to previous notes in our column will show trouble has been eaused by defective joints. sinnand

Joints must be clean, all paint or enamel must be scraped off and the surface polished with sand paper. If an earth clip, which is the best medium for making a connection to a waterpipe, is used, it should be tightly clamped to the pipe. If wire is wound round it should be drawn very tight and covered to prevent corrosion. This, however, is an unsatisfactory joint. Avoid the use of joints in the earth lead or aerial systems. If they are inevitable they should .be soldered. Twisting wires together may serve temporarily but will lead in a short — time to lower efficiency. Numerous lead-in wires are only twisted to the aerial. Sooner or later this must cause trouble. Corrosion takes place, signals fade out, come in intermittently or become very weak. ‘This denotes defective joints and requires immediate attention. ‘ It is important to see that the aerial is so rigged that it is not constantly chafing with the action of the wind ; an aerial which is allowed to swing too much is apt to break some strands ot the wire of which it is composed, producing unpleasant crackling noises in the set. Dirty Insulators.

NOT infrequent cause of leakage and consquent loss of signals is | dirty insulators. After a.time, especially if the aerial be near a railway line where the smoke nuisance is manifest, insulators become caked with a covering of deposit which is usually a good conductor. Bare wires passing through > an insulator thus rendered imperfect, are able to form a contact with staywires and conseqeuntly to earth. Trouble arising from this source will be: more in evidence in wet weather when the coating becomes damp and its conductivity is improved. Seaside dwellers may be troubled with the reverse, good reception during wet weather and poor reception during dry weather. This could be accounted for by a coating of salt forming on the insulators and forming a bridge to earth. During' wet weather this would be washed off leaving a perfect insulator. It is well worth while inspecting and scraping insulators periodic-ally-this may save a great deal of trouble later on.

TITITITIITITITITTITITITII I hha Notice to Beginners and Correspondents.

(1) Readers in difficulty or who have solved a difficulty which may be of interest to others are invited to write to us. , (2) Questions of general interest will be answered in these columns, those referring to construction will be referred to "Pentode." (3) All questions not of general interest must be accompanied by a stamped and addressed envelope, for individual reply. (4). Address all correspondence "Observer," Radio Record, Box 1032, Wellington. (5) Where a query refers to trouble which cannct be located the following: information should be given:(a) Name and model of set if factory made. (b) A diagram of layout if home constructed. (c) Particulars of valves, voltage, and grid bias. (da) As many other details as readily available.