WIRELESS NEWS.

Press, Volume LXI, Issue 18479, 5 September 1925, Page 5

WIRELESS NEWS.

GOOD RECEPTIONGETTING THE BEST RESULTS. (SraCIALLT TTBHTSS tot. '"TILE PRESS.")

(By "Eleetra.")

There is a large of radio enthusiasts whoso chief ambition is to get clear and undistorted reception, regardless of volnme. They are interested in radio lor iho programmes which it brings to them, and if these are not produced faithfully, without ho*vls or scratches or hisses, much of the joy of owning a radio set i> lost. It is for this group that tho following advice has been written. Thero is a method in perfect, or near-perf™ t, reception, and by following the rules it limy bo obtained. First of all, poor quality in receiving may bo attributed to any number of causes, including leakage of energy, poor wiring, inferior condensers, in.orjeet grid-leak, and grid-condenser vaives, inferior valves, or tho v orkin,, <if any valve at an improper portion or i its curve, use of too much regeneration, poor loud-speaker or 'ph nos, and incorrectly designed or inferior transformers. , i In all the circuits, oxcept the yg"*" I ing battely circuits and tho ,'oads to tho 'phones, tho wiring should ho «« short and direct as possible. Wrier wires run parallel they should bo wcl spaced. All connexions should lie we.l I soldered, to prevent tho of a cklings una come from .loose joints. | Leakage in tho apparatus and oej twoen the different parts of a set is most annoying to tho person j who is striving for quality when it is ■ irregular, and allows discharges to take place intermittently. This type of trouble might be found most frequently in tho variable condenser insulation and dielectric. Sometimes, too, it is found in tho paper dielectric of small fixed condensers —tho pores of the paper making the electrical stress uneven. Condensers. These paper condensers also cause much of tho instability of regeneration, with its accompanying howling. Unless the dielectric is uniform throughout, and both the plates and tho dielectric are held securely together, both change of capacity and leakage are bound to occur. Most paper condensers are variable over a wide range by simply squeezing them. If a set professes to be good do not tolerate this type of condenser.

The grid-condenser capacity is quite important, and usually the best valuo is somewhero between .00025 and .0005 mfd. The valve container and tho circular which generally goes with the valve usually tell the besjt valuo of condenser for that particular tube. Somo recommend variable condensers for this place in the circuit, but tho avorage tube now in use is not critical enough to allow any great advantage commonsnra'to with tho additional expense and trouble.

The correct valvo for the grid-leak also is to be found on the valve carton or circular. This is an instrument which may be made variablo to advantage, for although for a single class of work a single setting ctf this valve should last throughout the entire life of a given tubo, for local and long-dis-tance work it is sometimes better to us© different valves. Weak stations require greater resistance than strong stations. Standard Valves. Often too little attention is given to the question of the valve. It is imperative that 'this be the best, for upon this the entire working of the rest of the set depends. Unless you have plenty of monev with which to experiment, tha standard valves are the only ones to be used. The apparatus for making tubes is exp2iisivp and complicated. The designing of valves must bring in the resulls of years of experimenting by compi-tmit engineers, and the 'actual construction entails the services of the highest grade of workmen. One may. be sure that tubes coming from concerns whose' reputations are doubtful cannot be the highest grade products. Hie valve is worked at an improper portion of its curve when you use an "A" or "B" battery that is too lrgh pr two low in voltage. This causes either weakened signals or distortion. Your valve carton will tell you the proper voltages, and it would be we!' to abide by. them. Amplifier tubes have quite a latitude of "B" battery voltages to choose from, Wu the detector can seldom taks more than 22$ volts. Turning up the "A" battery rheostats will cause disagreeable noises and howling. The use of too much regeneration is an evil to which most radio set owners are addicted. The howling that conies in with distant stations is oaused by just this. It is a sign that your set is not capable of reaching that far without getting the tubo into oscillation. The onlv remedy is to add radio frequency amplification and cut down the regeneration. This will give you qnality as well as distance. Speakers and Head Sets. Loud-speakers and head-sets are very important items to be considered when striving for quality. As was mentioned when speaJcing of tubes, the reputation of the manufacturer should go a lonpr way in helping one to choose these articles. The construction is by far the most important point. The strength of the magnets, the separation of the pole pieces from the diaphragm, and the diameter and th'ckness of the diaphragm are all quality-determining factors. In most instances a unit for use with an amplifier and horn ehoyJd have provision for the adjustment of the separation of the diaphragm. When this 6nace is too close, the diaphragm rattles against the pole pieces, and when it is too great the volume is more than commcnsurately reduced^

! Transformers. | As with 'phones and tubes, trans- ! termers require careful designing and construction. There are a dozen or so makes on the market, with just several of them that are really worth while. Choose them carefully, according to instructions that liavo appeared before in these pages, and pay cspcial attention to the ratio of turns and tho resistance. Mount them as far apart, and at right angles. It thev aro suicided, it i s the best policy to connect tho shield to the ground-post ol the set. \ USEFUL HINTS. • "H', £oles in composition panels i enough so that the ■ crows fit loosely to prevent binding, after boles are drilled in n panel and the instruments aro ready to be assembled, tho panel cracks when tightening up the screws. Base-boards also are often split by the screws used io Hold the various instruments in piaoe Tins is particularly likely to nappen if there are several screws 'near together which are in line with the same grain in the wood. Avoid this by scattering the screws as much as possible When the valve does not fit properly »»?" * oc k c t. a toothpick or a mat-h whittled down to form a wedge can be placed between the socket and the valve to hold it tightly in place. CORRESPONDENCE. .'■lgnorant," Rakaia.—(l) Certain soil conditions, such as sand, very dry earth, or shingly soil, will give poor reception, but in New Zealand really . c f^ s aro few and far between. )} n nrst-class 6et would Oo6t about £4O complete with valves, 'phones, loud-talker, and batteries. This does not include the aerial, which can cost anything from 10s to £lO. As a rule in the country, tall trees handy k"* j- e are made use of for svspendiric; the aerial, thus saving tho cost of a 40ft Oregon pole. (3) Buy it every time. You would not think of purchasing a gramophone in parts and building it up if you did not knoTv anything about it. The same applies to radio sets. The Crosloy Trirdyn Reflex Set or Neutrodvne should give you the best resu'ts. (4) Unless yon know the theory of radio, I would not advise you to do so. The aerial you could no dotrbt erect yourself alter being shown.