FOR RADIO LISTENERS.

Hawera Star, Volume XLVI, 29 September 1926, Page 6

FOR RADIO LISTENERS.

RECEPTION EXPLAINED HOW TO AVOID HOWLING VALVES In the hope that an expert hut simply worded explanation of the process of radio reception will he of value to listeners generally, and especially to novices, wliose handling of their sets may interfere seriously with others in the locality, The Star has arranged with an amateur of long experience to place his knowledge and advice at the disposal of readers. The article printed helow will he followed by another next Wednesday. (By Senex.) By the recent completion of the stations in Auckland and Christchurch, the radio broadcasting of musical programmes and other items of interest has started in real earnest, as far as New Zealand is concerned. These stations are of the latest type, and, although not so oowerful as those of Australia, they* are putting 'up a highly creditable performance, so much so that Auckland can be heard in Hawera during the afternoons at a strength equal to the much-, more powerful broadcasting stations in Australia during the night time. As a general rule, wireless reception is better at night. With the excellence of the Australasian wireless, stations, there has been a stimulation of the public interest. It is the common talk, and already la roe numbers of receiving sets are being installed. When it is considered that there are over 2,000,000 of licensed receiving sets in Great Britain a, proportion of approxiniately one to every twenty-four. of the population —in a rural country like New Zealand it may lie confidently predicted that this proportion will be exceeded. So many people will he entering into this new sphere of social advancement that it might be useful to rutrover, the different types of receiving sets and give some elementary information as to wireless reception.

A wireless broadcasting station throws out into the air a stream of waves or vib ration s_ along which speech and music is carried. These waves can be received by (1) an outside aerial or wire suspended in the air, free from contact with other objects, and led through the wall of the house to a receiving set situated in a room or hall; (2) by an indoor aerial similarly disposed, except that it is inside the house instead of in the air outside; and (3) by a loop, which is an arrangement- of wire wound on a large frame, doing away with an aerial and requiring a specially sensitive reooiving apparatus. With the first two methods a suitable .earth or ground connection is required. Each broadcasting station has its particular length of wave, so that, by means of a coil and tuning condenser in the receiver, one- station can be separated from another. There are over a dozen of these stations operating in the vicinity of New Zealand, arid l six or eight of those can be easily by the most simple of receiving sets. - When the aerial is “tuned” to the selected broadcasting station the signals pass through a. “valve” in order to get audible music or speech. It is not intended to give a full description of valve action in the meantime. Let it suffice to sav that the valve acts as a- rectifier, enabling the wireless vibrations to become intelligible to the human ear. So that,, to get- music or speech from the transmitting station, the essentials required are an aerial (or collector), a means of tuning (or separating one station from another), a valve (for interpreting the signals), and a pair of head telephones (to hear the signals). When it is necessary to increase the volume in order to Avork a loud-speaker, which' will intensify the sounds equal to an ordinary gramophone, an amplifier is added in the receiving set. This, generally consists of two more valves, together with small transformers, which build im the faint signals received at the rectifying valve. The signals are now sufficiently powerful to fill a room with the music from the air. Owing to the distance one has 1 , as a rule, to cover under New Zealand conditions, ftis advisable to build up the signals still more. For instance, in Ha wera a distance of at least 200 miles must be covered, and also a sufficiently powerful receiver is required to get Australian stations in satisfactory volume. The best way is to liawe a fourth valve, placed before the rectifying valve. This is called a radio-frequency valve. Tt “boosts” up the incoming signal at- a frequency above that which can be detected by the ear, and the signals must he rectified or .boiled down by .the rectifying valve before it can be heard as sound.

A modern receiving set will, therefore, consist of a tuning arrangement, a radio-frequency (above audibility) amplifier consisting of one or two valves, a rectifying valve, and finally an amplifier for getting increased volume a.t audible frequencies. This all sounds very terrifying. However, the ingenuity of the manufacturer has made it all very simple. As a matter of fact, it is the basis of a most- popular form of receiving apparatus culled the Neutrodvne.

Another means of getting increased strength of signal is hy the use of what is called “reaction” or “regeneration.” This is a means' hy which'the signal, 'after initially passing through the rectifying valve, is fed hack to the receiver, so that, when it passes through that valve once more, it is increased in strength. The feeding hack process occurs again and again, until the valve refuses,to handle anv more. When this happens the valve howls lustilv. Reaction is obtained hy means of a special eoil which is movable, arid it is difficult to control smoothly. Herein lies a tale. The rough usage of reaction methods constitutes a nuisance to the person .operating the set. and not only to himself hut to others in the- district. For when such uncontrolled reaction is used, in an endeavour to receive at greater signal strength, the apparatus then energes the aerial. In other words, the receiver becomes a< small transmitter, and squeals and howls are sent out into the air, interfering with reception at one’s own particular set. and unfortunately affecting other receiving. sets quite a distance away. These notes are written as a special appeal to those people who have- receiving sets of the type using reaction. The amount of valve howling in Hawera is appalling, and it is getting much worse lately. Those possessing Neutrodyne sets are happy in the knowledge that their sets cannot possibly cause interference —if the sets are properly neutralised. For those possessing the other type of receiver a few instructions as to proper manipulation of their sets may not he out of place. To force a receiver to the extent of making the valyes scream does not help the reception of breadcast in any way whatsoever. In fact, it distracts the signals

so badly that little sense can be made of them. The more noise that it is possible to make seems to he the height of ambition of the unintelligent operator; but let him clearly understand that, by having his set oscillating so violently, he is interfering with the proper operation of receiving sets a- good way off, as well as spoiling his own. If there is a stage'or two of radio-frequency amplification before the rectifying valve, so much the worse. When a broadcasting station is tuned in, the scream of the “carrierwave” will be heard. (This would not be heard with a neutralised receiver.) Moving the tuning dial -GENTLY (big letters, Mr Printer, please) backwards and, forwards will elicit a dead spot in the middle of the carrier-wave. It is here that speech or music will' he heard. One can generally clear up the music by moving the reaction coil away from the coil with which it is in proximity, and moving the reaction condenser dial (if any) gently, very gently. If there is a loud howl, or series, of screeches, or a loud scrunching noise from- the loud-speaker, it is a clear indication that the reaction coil is too close, and it must be moved further away. The , set is , oscillating violently, will not receive music without mushing or distortion, arid the howls are being gathered up by other receiving/ sets and magnified hy. them, not- entirely to their amusement. The proper adjustment and correct distance of the reaction coil will he attained when, a slight hiss is heard in the head-piece or loud-speaker when the tuning dial is moved' -slowlv to and fro. Next Wednesday the subject will be referred to again, and other finer adjustments described. Opportunity will also bp taken of answering any questions of interest to broadcast listeners.