Summer-Time Radio

Radio Record, Volume III, Issue 19, 22 November 1929, Unnumbered Page

Summer-Time Radio

Time for Picnics and Portables

UMMER immediately conjures up visions of grassy | banks, shady trees singing birds, delightful beaches, and gto the radio enthusiasts a good portable set. The optimist thinks at once of some delightful spot miles away from the dust and roar of traffic where he can sit after lunch and listen to the music of his home. station. The pessimist dwells on the hopelessness of trying to enjoy oneself with a portable receiver, unless there is a car within close range to carry the "‘thing’’ home, of an obstinate fire which will not burn with wet wood, of mosquitoes and of dust. When both sides of the case are considered, however, a good light, efficient, portable receiver adds to the enjoyment of picnics and excursions. Most of these parties nowadays, when within reasonable range of home, take a portable gramophone, *but from the limitations necessarily imposed it can be seen that the wireless set, which embodies many of the better features of the gramophone, can yet be more popular. Good reception can be assured when reasonable precaution is taken, and when a moderately good circuit is employed. Of course there is. the very troublesome question of batteries for good reception, apart from high voltage, and heavy current drain, cannot be fully realised. One must be prépared to make certain compromises; he must not expect reproduction such as he would obtain from his multi-valve receiver with its power amplifier and dynamic cone speaker. The fact of being able to receive news from the home town, or music from the nearest station is alone a good enough incentive to warrant the presence of a portable receiver. Excellent receivers may be purchased and no doubt very many picnicers ‘will be prepared to obtain their portable in this manner rather than go to the trouble of designing and building one. In such a receiver problems that we are going to discuss will not be present, but without a doubt the greatest fun comes from using a receiver that one has designed and built, rather than one which has been purchased "ready made." The first problem presenting itself to the operator of both commercial and home-made portable receivers is the aerial. In nearly every, case these receivers are equipped with a frame antenna which is no more than an enlarged grid coil built into the lid of the receiving cabinet. The use of this type has decided compensations, although it will undoubtedly be weaker in signal strength. During summer months there are quite a number of storms and occasionally some of them are very severe. When an outside antenna (aerial) is used very many people are afraid of the lightning danger. Actually, this is. very remote, but nevertheless a lightning arrester should be placed in series with (Continued on page 2.)

Come Summer go Radio isa: maxim not without foundation. Due to the sresistible claim of the beach, the receiver is forgot: ten and remains behind untended while the crashes of static, unwelcome concomitants of summer, break harmlessly through. Whether outdoors or ‘in, music brings cheer and musical instruments can usually find an opening im every pleasure party. For this veason .gramophones are popular, mm spite of the fact that they entail the transportation of numerous and breakable records. Just as this instrument has earned popularity so the future of the portable receiver is assured.

Music, news, weather reporis-these add to the pleasure of any camping party and they can be brought only by radio. Portable sets are in demand, and to meet this need our next issue will be devoted to the: description of two portable recewers. One is so compact that tt can be placed in any tramper’s pack or camper’s supplies. It will give good *phone reception of New Zealand and Australian stations and loudspeaker volume from the local. The other is ideal when the’ car is taken. It 1s stronger and when used with an aerial will bring in even the big Australians on the speaker. Yet both these are easily constructed.

Summer-Time Radio

Portables for Picnics

(Continued from front page.) the aezial to act as a safeguard. As a matter of fact there is a clause in .- the rules of the Fire Underwritters’ Association which tightening danger, Actually, this is very remote, but nevertheless a light-ning-arrester should be placed in series with the aerial to act as a safeguard. As a matter of fact, there is a clause in the rules of the Fire Underwriters’ Association which protects fire insur‘ance companies against fire caused. by induced charges from an aerial. . In other words, if & fire occurs and it can be proved that an aerial leading into a radio receiver was not equipped with an arrester, the owner of the property has: no claim for insurance money. _Another bugbear of summer-time reception is the prevalence of static. In sultry weather one often hears so many crackles, crashes, and other delightful noises that distant reception becomes painful, if not impossible. Quite frequently, too, the programme from the local station is marred, Atmospherics are due to waves of no particular frequency set up by lightning discharges often very many hundred miles away; the louder crashes are often produced by local static charges collected by the aerial and discharged through the Set. HIS brings us to the point where we diverged. The use of a frame antenna for summer-time reception minimises static and does away completely with the lightning question. There is a very much quieter background, selectivity is sharper, reaction usually smoother, and the receiver may he used even when a thunderstorm is overhead. Apart from use of portables, frame antenna may with advantage be used.in the home. Details of such an antenna will be found in our special number next week. When conditions are good an aerial can be used with advantage with the portable receiver to replace the frame which then acts as an ordinary grid coil. Signal strength is strengthened, with the result that stations that could be heard on the *phones can now be put on the speaker, and very many more brought on to the

*phones. Almost every portable receiver is designed so that an aerial may be attached. Well-insulated wire such as "electron" may be purchased very cheaply in 100ft. rolls, and a single rol) of this wire and an insulator or two, a copper earth tube with a wooden mallet _ to drive it. into the ground and a small Wireless set will entertain quite a very large circle of holiday makers. In reception of this nature where _ rapid changes of location are neecssary a few refinements should be made to the aerial and earth equipment. Tie an insulator into the centre of a fairly long piece of cord, pass the insulated wire through insulator and secure it by a convenient knot to the aerial itself. This may now be suspended from, any convenient tree or other support. The particular merit of this device is that the end of the aerial can be quickly attached to any-convenient point, while the same end of the aerial is well , insulated from the object to which it attached.

The fact that the wire is insulated does not always dispense with the use of insulators. ‘The insulation of the ferial wire, while excellent, is thin, as if this wire is bound round, for ¢xample, a metal post corisiderable leakable of witeless current. can eceur from the wire to the post, The insulation here acts as a dialectriec of a quite large condenser. Aerials may be slung from tree to tree, and a lead-in provided, or one end may be hoisted in the air and the other direct to the set. The aerial may be slung over a convenient support, and although both ends may be resting on the ground provided they are insulated from it good results will accrue, A wire fence makes another very good aerial, for in very few cases. ure the wires earthed, It is advisable, however, in cases where either this or any other large object is used as antenna. to connect .2 variable condenser of sinall capacity between the aerial terminal of the portable set and the aerial. This can then be adjusted so that the best results may be obtained. Such. condenser built into a box is an essen- tial to any complete portable outfit. The body work of a motor can he brought into commission and makes a really useful aerial. It is wise, further, when using a motor-car in this manner to keep the set either well away from it or place the set so that the car is not between it and the station that is to be received. This shielding effect of a motor explains why a portable set may not work when inside, A motor may be used for another useful purpose when holiday making with a portable receiver. The American ears are provided with 6-volt batteries for the lighting and ignition system, and by plugging into the nearest socket power may be taken off for the A battery, which is the greatest bugbear of portable receiver Mesign. OBTAINING an earth occasions very littlé difficulty, but to obtain a good earth requires a little thought and preparation, An earth tube driven into the ground is excellent, but: to drive some of these into hard soil and pull them up again often militates

against the enjoyment of an ner pienie party, A nail driven into a liying tree so that, it connects with the sap makes an excellent connection with the ground, while a copper or metallic mat thrown into a stream makes a both convenient and ideal earth. Two waterpipes driven into the ground at some distance from one. another may be used for aerial and earth. This is possible because the ground potential at differ. ent points varies, Harth mats (large sheets of copper and bronze gauze or netting) ‘were largely used during the Great War. When these are unrolled on the ground they can be used as counterpoises, and will often give.much better earth effect than a varied plate, particularly if the latter is small. An earth mat may be a mattress spring, can be rolled up and tucked into the back of a car, and ole should certainly be obtained if 9 ay serious effort at outdoor reception is contemplated. HEN a wireless set is designed the enthusiasm immediately thinks of screen grid and pentode valves. With the enormous amplification factor that these possess, it would: appear that these are the perfect valve for portable receivers, but theree are one or two points to consider. Both valves require high voltage to. operate them successfully, and the-secreen grid requires

very complete shielding: The pentode does not operate successfully, if supplied with low voltage, and even when adequate voltage is forthcoming, then a very large current drain results. By object of portable receivers is to kee’ both these to a minimum, so that we consider it unwise unless adequate battery power can be provided to incorporate these valves in the summer set, at least in the smaller set, The total current drain for economical use should not be greater than ten milliamps. The power valve should be biased so that it will accommodate a fairly wide grid swing, although it need not be efficient as the power valve in the radio receiver used for home use. Good reception is required, but that supplied by a sensitive speaker i is to be preferred to good quality and a lower volume level supplied from. a good cone, for this reason, a horn. speaker is better than a cone for outdoor reception. Microphonic trouble often- arises. A ringing will start in the speaker. and gradually build up until. the noise is. unbearable, and the set. has to be shut oF Most detector valves are -microphoxie to some extent, but this is not noticed in the home where good conditions may be secured. When, however, the set is frequently moved or the surrounding objects moved, the trouble frequently becomes acute. A good preventive is to cover the valve. with plasticine, which, although effective, is unsightly. The screen grid valve . occasionally eauses trouble in this manner, but nothing so usual as the. fletector, The use of the detector. mikes these pre"uutions unnecessary. The unforgivable sixi--allowing the ‘set to fail thr ough fat batteriesshould never be committed; ’ There is no excuse for it. although it probably more disappointment ‘than any other factor. No matter how.well a set may be going the diy or-the night before, put the voltmeter across all ‘batteries before setting off, and replace any that. are at all suspicionsly low. For "A" current,. the use of dry cells is usually resorted to, but an. atcumulator is preferable, and should he used

irk conjunction with valves of a low filament consumption varying from .06 to .1 amp. radio may be a pleasure-it may be an annoyance, but if proper preeautions are taken and simple advice followed, it can add very much to the joy of picnic or beach parties.