A Corner for Beginners

Radio Record, Volume II, Issue 21, 7 December 1928, Page 10

A Corner for Beginners

By

Observer

wont ne seuwsticeontnaasentititinaito Trouble with Crystal Sets. Hi following interesting letter dealing with trouble finding, has been yeceived from A. C. Loach (Christéburch) :- "tT notice that in the "Record" you vepeatedly impress on owners of small sets the need of an efficient aerial and earth system, but apparently with some people it does not sink in very far. Friends often bring crystal sets along for me to overhaul, and as a rule when I hook the sets to my aerial they are quite efficient. So then I return the set to the owner with some free advice on the care of the aerial. In nine cases out of ten lightning conductors are the cause of the trouble due to corrosion at the terminals. Other eauses are leads-in unsoldered, and ground wires unsoldered. The most striking case I dealt with was that of a fellow who moved out our way from the city. He brought

his set along to me with the usual tale of woe, "It won’t go!" Hooked it up at my place one evening and the result was terrific 3YA came in with a great rattle, and was quite audible on the speaker direct, and from the crystal whilst on a two-stage amplifier it was beautiful. 2YA was clear and distinct on the erystal alone. I began to get

interested in this set, so when 2YA closed dewn their news session 1 connected the amplifier up dnd landed 2FC on news. Waited till 3YA closed down for the night and then bagged the following :-2FC, 2BL, 3AR, 3L0, 4QG, 2GB all at good ’phone strength, except 2GB. mo, I wrote out the list of stations heard also names of various items announced from same and handed it to the set owner with some more advice on aerials, etc. His aerial comprised a 100ft. length of wire from the top of a 80ft. pole on to a chimney, lead-in twisted round aerial wire, not soldered! The earth was a 2ft. of galvyanised pipe driven into stony soil. ' My own aerial is as follows:-A single pole, height 56ft., with an ordinary telephone pattern insulator at the top. The aerial wires radiate out in four directions from the insulator, act-. ing as the top stays for the pole, the lead-in being taken from the lead nearest. the set. This type of aerial should be ideal in cities where enthusi-. asts are cramped for room. The earth used is 4ft. of copper piping. buried in cinders. | The method of erecting is to place a 15ft. length of oregon, 6in. x 3in. with its two hardwood legs 18in. to 2ft. in the ground and then to place the 40ft. pole 3in: x 3in. alongside, and secure. with the clamps. Secure the stays and slide pole straight up through clamps slackening stays as required. The aerial wires are carefully insulated to prevent contact with the lower portion which acts as stay wires. The whole is like an umbrella. I hope this will be of some interest to you, and wishing you the best of luck in your good work." This is certainly of interest, and the letter is passed on to listeners. with the writer’s commendation. The aerial should be very useful in congested areas. Undesirable Conductors. A CORRESPONDENT writes of a peculiar source of trouble which caused him -great expenditure and much delay. At the end-of the usual programme the station closed down and his receiver was perfectly in order, but on attempting to tune in the following day it was found that the signals were painfully weak, too weak to satisfy the loudspeaker. The usual channels were searched without avail. An expert was summoned, components replaced, yet no improvement. Finally a most inoffensive-looking spider-web was discovered between the lead-in and the ground connection, both of which were bare. On sweeping this away the set went as though nothing had happened. : | Spider webs have extraordinary conductivity and should be kept clear of all wireless apparatus,

WHILE as a rule rain makes not one ; iota of difference to a properly insulated aerial, it sometimes happens . that during a rain storm (or even only part of the ‘. .e) a loud noise, fierce and crackling, will accompany the rain. On such occasions it may. be taken for granted that there is a certain amount of suspended electricity leaking to earth through the.rain. Dirty, ineffective insulators have "heen known to cause a similar effect. | Electrical’ Measurement. A WORKING knowledge of the fundamental relation between ‘volts, amperes, and ohms, the three basic units of electrical measurement, will prove useful.to the radio beginner. The volt. is the unit of electrical pressure ; the ampere, of volume} and the ohm, of resistance. In any electrical circuit, the voltage or pressure is what forces the amperes or volume through the ohms or resistance, It takes one volt to force one ampere of eurrent through a resistance of one ohm; hence you can figure the current or amperes in any Circuit by dividing the voltage or pressure by the ohms or resistance. Similarly, you can figure out the resistance of any circuit by dividing the number of volts. by the number of amperes, And if you wish to know how many volts would be required to force a certain number of amperes through a specified resistance, multiply the number of amperes by the number of: ohms, Positive and Negative. JLECTRICITY as we understand it is of two kinds, positive and negative. The positive tends to flow to the negative and the negative to the positive. The attraction of the positive pole is strong enough to entige the negative electricity through the entire radio set. The positive flows to the , negative through the battery, which is" composed of ‘little cylinders of zine (-), a paste and a central rod of carbon (+).: | | If the -++ pole, which is usually eoloured red on accumulators, marked. +. on dry blocks, or in the: centre of 14 volt cells, is connected to the negative pole by a low resistance, comparable to connecting an empty tank to a full one by a wide pipe, the electricity will rush from one pole to the other at such a rate’ that before long the power will. be -lost.. ) ° If connected through: the set, or through the high resistance filament of the valve, the flow is slow and the cells last longer. The flow is caused by a chemical reaction being: set up in the zinc, paste and carbon. A battery is in no sense a store of ‘electricity, it is a manufacturer. When the manufacturing elements. become worked out the battery does not function, To. renew it the elements, zinc and paste, for carbon does not rapidly deteriorate, would have to be replaced. This is virtually a new cell. Testing Polarity. J view that electricity flows from the negative to the positive, ovttside the cell, it is necessary, then,’ that the positive be connected on to the ve terminals of the set, those designates by the designers: as"being the most appropriate for receiving the current. This usually presents no difficulty, as the batteries, accumulators.or eliminators, are always clearly marked, while ~ terminals on the set are always marked and wires usually coloured and labelled. One. word of warning-don’t.connect ap batteries in a.dark cupboard. by