Questions and Answers

Radio Record, Volume II, Issue 26, 11 January 1929, Page 11

Questions and Answers

IN BRIEF, FERGUSON (Dunedin): If you *forward an addressed envelope we will forward you suggestions as to how harmonics may be cut out. G .C.T. [* our last ‘issue, a correspondent asked for the meaning of the abbreviation G.C.T. At the time we were unable to verify the information offered us with the result that an inaccuracy has crept in, It appears that G.C.T. signifies Greenwich Civil Time. This term, identical with G.M.T., is used to compare American standard times, so that announcements made regarding the times of transmissions of important news, reports, ete., are stated in G.C.T.. Hach Time Zone can make its own adjustment. Thus one time is announced instead of several. Greenwich time is chosen beeause it is accepted as the standard time of the world. A chart enabling the rapid conversion of time has been published in the Radio Record. The time zones in America are Atlantic Standard Time. (A.S.T.), Hastern Standard Time (E.S.T.), Central (C.S.T.), Mountain (M.S.T.) and Pacific (P.8.T.). Dial Markings. I have a factory built 6-valve set, and, on the front, in a semi-circle is un indicator marked from 0 to 100. What is puzzling me is that, say 2YA is advertised on 420 metres, how I can get him on my wireless. Do these marks represent so many metres? If 30, what is the correct method of obtaining 2YA on 420 metres?-PUZZLED (Wanganui). ANSWER: The question as to why 2 station operating on a certain wavelength can be brought in at a different number on the dial has puzzled many. Behind each dial is a condenser or several condensers fastened together (gauged). Of these there are two principal parts, the moving plates and the fixed plates. The moving plates move in a semi-circle, hinged, usually, slightly to one side of the centre, and the amount of the moving plates passing between the fixed plates is thus controlled by the knob on the panel. When the moving plates are right clear of the others, it is clear that one limit of the semicircle has been reached. As no proportion of the, moving plates is between the fixed plates the reading is 0, while, when a semicircle has been described or 180 ‘degrees passed through, all the plates are between the fixed plates and the reading is 180. This action of the condenser has the effect of altering the tuning of the receiver to make it sensitive to a band of wavelengths which are determined hy

the coils. The usual range is between 200 and 550 metres, so that a station of 420 metres would be brought ,in at some of the higher numbers of the dial, There is a* method of calculating where stations can be found from their wave length, but it is a task that may be a little formidable to anyone who has not had practice in elementary mathematics. The best method is to keep a log noting the position and the wavelength of the station received s9 that when it is desired to hunt for a stranger whose wavelength is known, the proximity can be ascertained by reference to the nearest station, in point of wavelength, that is heard on the set. Points About the Aerial. J. K.M. (Kai Iwi) writes: As a heginner, and . keen follower of "Questions and Answers" in the "Radio Record," there are one or two points I would ask you about my radio set. The type I have is a factory made set, aud the results I obtain are most satisfactory, yet I feel I can better my reception in some ways and am keen to try, hence my reason in enlisting your aid. Interference is practically nil as there are no high-power lines within three miles and no surrounding obstacles, such as hills, bush, ete. Altitude, roughly, 1000ft. Reception from 2YA is just about perfect, 1YA comes in fairly well, but 3YA and 4YA are rather indistinct. I am enclosing two Tough diagrams which may help my crude explanations. (The diagrams are good and help materially to make the meanings clear-Obsr.). (1) My earth wire is now 9ft, long and insulated. Would it matter if it were lengthened to about 18ft? ‘This alteration would shorten my "lead-in." ANSWER: The general rule is to keep the earth lead as short as possible so that unless there is no other way out of the difficulty, do no lengthen. (2) My lead-in is not insulated at present. Would it improve reception if I replaced it with insulated wire? ANSWER: The lead-in should always be insulated as it is usually necessary to pass this near to a roof or to the side of a building which will act as an earth and lessen the effective height of the aerial. (3) Do you agree with my alteration of the lightening arrester to keep it dry? If moved it would be up under the overhanging eave and hence more sheltered from the rain, ANSWER: From a sketch, the writer shows that the arrester is fully exposed to the elements. ‘This is a bad plan for sooner or later the dampness will find its way into the "works" and cause a short to the ground, thus seriously impairing the efficiency of the aerial. This may be happening at the present time and be the cause of the unsatisfactory reception of the more distant stations. The new place suggested, under the eaves, would be much more satisfactory. (4) Do you consider my earth sufficient? If not, could you help me by suggesting a really efficient earth? ANSWER: The earth, while not particularly good, should be quite satisfactory. Suggestions as to how the earth might be improved were made in our special issue, December 14.

(5) I have taken bearings in connection with my aerial wire and the direction is roughly North-North-West. Will this bring in the best results? I propose erecting new masts shortly and so can put the new ones in the correct position if that would be better. Are the present masts (42ft.) high enough? ANSWER: The aerial (a T) is directional to the New Zealand stations which is probably the best, as real entertainment is to come from the local stations. If the Australians are desired in greater strength and the New Zealanders can afford to be weakened, try running in a north-easterly direction. Yes, the masts are a good height. If these suggestions do not aid the correspondent to solve his troubles, he would be advised to make a test of his transformers, condensers, chokes, valves, ete., by the methods frequently described in the SBeginner Corner. Help in this direction will supplement the notes, if any specific difficulty is encountered. Amplifier to Work from Mains. "PENTODE," Friday, November 16. shows diagram and particulars of erystal and amplifier to work off A.C. mains. In the use of erystal this works very well. Should a valve be used in place of crystal, what alterations or additions would be necessary to obtain, say, 224 volts (as used in conformity with B battery) ?-C.W.B. (Wellington). The receiver is not suitable for adaptation as suggested. Correspondents making up this receiver should exercise great care, for there is a certain danger in working with the A.C. current. A Variable Grid-leak. "(COULD you inform me if there would be any need to alter a onevalve circuit if a variable grid-leak is used instead of a fixed. If so, could you tell me how it would be altered? I am at present using a 3 meg. gridleak, and I do not think I am getting the best-out, of the distant signals. "Ts it possible to publish a one-valve amplifier to run a Pentode valve. The Pentode valve is supposed to have a large amplification factor, therefore using a Pentode in a oneyalve audio the results should be far superior to an ordinary audio valve. Would the tone of the receiver. suffer with the increase of volume, and what B voltage would be needed to operate the

audio part of the receiver using @ en amen teed (Wellingon). ANSWER: A variable grid-leak can be inserted in place of the usual fixed type without any alteration to the circui Providing the correct voltage as stipulated by the maker is applied, a Pentode may be employed in a single stage amplifier. A suitable circuit was published in our special issue of December 14, page 28. Tone would not suffer, but rather it would be improved. What Tools are Required? AS I have never tried my hand at it, I should like to know what tools are required for building a simple set, and any details which you can give me about the right kind to choose." ANSWER: Very few tools are required, and the chief of these will*be found in the ordinary household toolbox. The following summary brings out some important points, which should be borne in mind if purchasing them :- . (a) Soldering iron (get one with a good, heavy end, not one of _ the light ones which will not keep hot long enough to use). (b) A tin of fluxite or similar soldering paste. (ce) A pair of cutting pliers. (Those known as side cutting are very convenient, but the flat-nosed variety are invaluable for tightening up nuts, etc.). (ad) A pair of round-nosed pliers, for bending the wire when it is required to put round terminal shanks, etc. (e) A flat file. (f) A hand drill for drilling panels, ete.,, and a set of drills for same. (g) A couple of screwdrivers, one fairly large, one small. There are many other tools whieh will come in handy later, such as vice, ete., but much depends upon the set you decide upon building. With the above you will able to make a very good start upon ordinary constructional work. , "TS copper wire better than iron for an aerial?" , Yes, copper wire has a higher conductivity than iron, and therefore is more suitable for aerial wire.