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A Corner for Beginners

By

Observer

An Earthed Aerial Works. ASs I am very limited for room to erect a single wire aerial, I have been using a double wire each 50 feet with 4 feet spreaders, height 35 feet. I am now erecting new aerial of heavier gauge wire with 7 foot spreaders, After partly. dismantling old aerial, not having time to finish, I gathered the two wires, from which spreader had been disconnected, drew them down tight and connected to pipe in ground, still leaving up one end with lead-in, and wires lying flat across iron roof. I still find reception as good as before in spite of aerial dismantled and one end grounded, distant stations coming in with great volume, Could you offer any solution as to why I should get these results with aerial as stated? — Also, kindly state whether, in erecting twin wire aerial, wires should be separate or could the one wire be passed through insulatoi, on spreader and back to lead-in end, twisted and taken straight down to set, making one continuous wire.-C.G.T. (Pt. Chalmers), Regarding the problem there are two points of view. : (1) That the roof was not grounded and that either of the earths were inefficient so that the aerial and the ground were. actually not in good electrical connection. The wire may have been loosely twisted round and so a poor contact may result. (2) Considering that the aerial was properly grounded it and _ the ground may be forming a huge loop, collecting signals in the same manner as does hte ordinary inside loop. Probably were the aerials to be reerected, it would be found that the signals were stronger than when the aerial was down. Wires for a twin wire aerial should be separated by six feet. The lead-in should be joined as near as possible to the set. This would allow a maximum of collecting area. Condenser Effect of Lead-in. IN view of the questions asked by our Marlborough correspondents, and answered in "Questions and An-. swers," the following letter and its reply, published in "Popular Wireless," will be of vital interest to those whose lead-in is suspected of being below maximum efficiency. A correspondent to this paper wrote asking why his reception improved when. he disconnected his lead-in, which ran round the wall, and temporarily replaced it by a wire coming straight in. The wire in the latter case was not so good. THE reason that you are getting bet- . ter results with the spaced-oud wire (replies the technical editor) is that formerly a certain amount of the energy that was passing along the lead-

in used to leak away to earth before it reached the set. Although -.you used insulated wire, the fact that it ran close to a wall set up a kind of condenser effect between the wire and the. earth. A certain amount of the highfrequency energy passed across this condenser, and found its way via this short cut to earth, without helping to strengthen the input to the telephones. By taking the lead away from the wall you prevented this short-cut effect taking place, and you have compelled all the current flowing in the aerial to pass properly down the leadin through the set to earth. It is because of such condenser effects between the wire itself and any neighbouring surfaces such as walls, gutters, pipes, ete, that it is inadvisable to run the lead-in near walls, ete. Never have a _ long lead-in if a short one will do. We certainly recommend you to keep it well spaced out from the wall or ceiling, if necessary using insulating, arms or wooden supports to ensure it is sufficiently spaced. Neutralising. ANY correspondents have written in complaining that their sets have commenced a peculiar whining. This seems to indicate that they have become deneutralised. ‘The following method of neutralising is recommended for use in sets employing one stage of H.¥F. and provided with a reaction control. Set the reaction control at minimum and likewise the neutralising condenser. Now, on setting the tuning condensers so that the two tuned circuits are in step with each other, it will probably be found that the set is oscillating. To test for oscillation, touch one or other of the sets of plates of the tuning condensers (this may be either the fixed or moving, according to the particular set). You will probably find that the set will only oscillate under the above conditions when the two circuits are in tune with each other, and this can be used as an indication. (It is convenient to perform the operation at some point near the middle of the tuning range.) Now, increase the capacity of the neutralising condenser. (In the case of such condensers as the Gambreil. "Neutrovernia" this means screwing downwards.) Test at intervals for oscillation as this is done, and you will presently find that the set has ceased to oscillate and will not recommence even when the tuning dials are slightly readjusted. Now inerease the reaction a little, until the set once more oscillates, and again increase the neutralising condenser setting until oscillation ceases. Slightly readjust the tuning condensers again to make sure that the set is completely stable once more,

SAUOSRSSSSRCHCUSSRERSSARDESASEGRESRESTSAATATSESTELSLETSTCSLIE2E9 Proceed in this way until it is found that the correct adjustment of the neutrodyne condenser has been over-shot. Once this point has been passed it will be observed that further increases of the neutrodyne condenser setting no longer stop oscillation, but cause it to become stronger. | . The object is to find such an adjustment of the neutralising condenser as will permit the greatest setting of the reaction condenser to be used without producing oscillation. It will then be observed that when the two tuned circuits are in step and the set is brought to the verge of oscillation a slight movement in either direction of the neutrodyne condenser will cause the receiver to break into oscillation. Note.-It is to be understood that in the preceding notes, where a reaction condenser is spoken of, any form of reaction control may be understood, A Useful Ground. B., writing from Dannevirke, sug- * gests a good ground. He has read our article on "Harths," in the special issue, and contributes the following as a suggestion. Three damaged motor radiators connected by heavy wire, and preferably to an underlying copper plate. The top of the radiators are ‘left projecting above the surface of the ground and are kept filled with water. An independent wire runs to each of the earths. including the copper plate. All meet at the binding post. "As the honeycomb arrangement makes quite a good contact with ground, which will ooze into cores, and a number of radiators are made of brass or copper, quite a good connection with ground should result. Bluestone or rock salt is also supposed to improve ground connections though I have not tried same." Soldering Hinis. To attach the lead-in, suggests A.B., first tin the pipe where the connection is to be made. Wrap the lead round this several times then solder all along the coil so made. To join two pieces of wire tin each for a distance of four inches from the end leaving 4 inch at the extreme end free. Bind with fairly fine wire, and solder again. Bend the two free ends back along the coil. "T consider the earth and wire joining connections worthy of publication, as I have seen figure 8 joins with a dab of solder in the centre called a good ‘join,’ also a wire running on side of pipe for 4 inch and soldered for earth connection." Heavy on Battery. A B. has advanced further suggestions * to deal with a set heavy on A battery.

— "I think F.M’s (King Country) article re ‘Heavy on A Battery’ worthy of note. Why not advise him to fully charge his A battery and let it remain unused and note how quickly it rung down? If it survives this test (that is, it does not run down), the trouble must lie elsewhere. The battery should be freed of wires in case of a short circuit in same. He may be using too much resistance in the filament circuit. I once ‘had trouble with my A battery running down, and traced the fault to a bad filament current Switch which was connected to an earthed metal shield surrounding the set. I found that on removing the earth wire the discharge ceased, although I have not as yet solved why. However, a new Switch put matters right. Set Loses Volume. " ANOTHER experience: My set commenced losing volume rapidly, and within a month was merely a whisper whereas previously it was audible (using five valves) 150 yards away in day time. But of course my aerial is 160ft. long and 50ft. high. On examining insulators holding lead-in away from wall, each one was covered with spider webs; on removing these the volume had jumped up to quite reasonable strength, but was still lacking. "I then suspected the earth, as valves and all batteries were O.K. On shifting the earth pipe (which was then used and only 3ft. long) to a spot a couple of feet away, volume was restored to normal, As I always watered the earth before turning in, it seems to me that I must have washed all the fine soil away, leaving only lumps in its stead. : Defective Resistance, e ANOTHER experience: I once was carrying out an experiment, using two sets (two and five valves) on the one aerial, using one set of. batteries. On switching on a burning smell greeted me; and clouds of smoke rose out of the larger set. I immediately Switched off, and on examination discovered that the reaction rheostat had been scorching, but apparently no damage was done. I then tried the five-valve singly, and it did not come up to "scratch." Some hunting ensued with no success, _ "Two months later a friend was conversing on resistances, whereupon I showed him my rheostat, and then removed the grid-leak for his inspection, and was explaining its works, and said: "See this strip of lead," and ‘on going to point it out found it was missing. A round blob of lead in one end of the tube denoted it once was in existence. A spare grid-leak was placed in the set, and all was as two months previously." HESE suggestions and experiences ‘are very helpful to others, and we thank A.B. for them. At the same time, we would like to hear more from others. Hveryone must have had some experience, or have some idea that wiil be helpful to others-send it in and make the "Beginner Corner" an "Exchange Corner." We are all beginners, and real progress can only be made by mutual co-operation,

This article text was automatically generated and may include errors. View the full page to see article in its original form.I whakaputaina aunoatia ēnei kuputuhi tuhinga, e kitea ai pea ētahi hapa i roto. Tirohia te whārangi katoa kia kitea te āhuatanga taketake o te tuhinga.
Permanent link to this item
Hononga pūmau ki tēnei tūemi

https://paperspast.natlib.govt.nz/periodicals/RADREC19281228.2.37

Bibliographic details
Ngā taipitopito pukapuka

Radio Record, Volume II, Issue 24, 28 December 1928, Page 11

Word count
Tapeke kupu
1,804

A Corner for Beginners Radio Record, Volume II, Issue 24, 28 December 1928, Page 11

A Corner for Beginners Radio Record, Volume II, Issue 24, 28 December 1928, Page 11

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