What Is Interference?

Radio Record, Volume VIII, Issue 44, 10 May 1935, Page 16

What Is Interference?

Listeners Must be Reasonable in Complaints- _ Responsibility of Users of "Noisy" Power ~ VER since’ broadcast receiving sets became a popular part of the furnishing in’ a large proportion. of homes interference has been a hurdle which called for strong language, deep thought- and extensive investigation in New Zealand as elsewhere. To-day, when so many have.powerful sets with which, they are told, they should receive Australia, America, even Europe, with a high degree’ of purity, listeners have, they think, grounds for complaint in many instances against the undue noise which. interrupts their enjoyment of radio reception. It is the intention of this article to inform listeners -as to: just what is considered to be a valid cause for complaint in this direction, and what steps have been and are being taken to overcome the trouble. The Broadcasting Board’s part of the solution has been to raise the power of its main stations. . :

LASt year, after considerable agitation, regulations were gazetted by Parliament which conferred upon. the Radio Branch of the Post and Telegraph Department the right to prosecute in cases where interference which was comparatively easily suppressible, wag not eliminated. Naturally, the public-particularly that section in every city and many country areas near trams or high-tension cables-inter-prets culpable interference in different ways, according to the individual! listener’s knowledge and common sense, In many instances radio. inspectors have been called in by . dissatisfied listeners only to find that the complaint is that when the set is tuned in to KFI or PCJJ there is plenty of really annoying electrical intereference, ani what would the department do about it? Firstly, then the interpretation of the standard of -unwarrantable inter.’ ence is based, sensibly enough, ‘on local station reception. That is to say, in cases where the _ electrical. forces of Nature spoil long-distance reception, no action could reasonably -be taken against those responsible for causing. electrical interference by some use of the power supply. Of course, when 2 source of interference is discovered which causes distortion in any sort of reception in a neighbourhood, the operator.of the device which is causing the trouble is consulted, but it would be frankly unreasonable to constrain him simply because his machinery ‘may be’ causing bad distant reception to a nearby listener. os As long as the nearest national! station of good field strength is re¢eived without interference, it: is considered by the department that ‘the listener is served with a trouble-free broadcasting service. That is the fundamental standard-and one which must in all reason be accepted at present. This standard means that the department is aware of the meaning of "essential" service to the average listener. Those who = purchase sets which are capable of long-distance reception must expect interference when they do switch ‘on to long distance: Nature sees to that in many instances; so who can blame’ the trams, electric motors and so on if they provide a little extra trouble? OW that we have Clarified the basis of tenable complaints, you might ask what the department is doing in the matter. In addition to extensive experimenting by technicians, the radio : inspectors in each district:are kept busy hearing the listeners’ point of view on

the subject of interference, and they have to locate the source of the trouble. Too often this source proves to- be. one which it may take months to correct, as in the case of tramway.lines, ‘or-even years, as when the high-tension, lines passing through a. country district prove to be the bugbear. Listeners who expect a correction of the fau lt to be made overnight are. therefore- due: for no small disappointment. A popular example, that of. trams. may well be analysed here. Officers of the Post and Telegraph Department found a long time.ago that the main

sources of interference in a tramway system were as follow: (1) Compressor motors for air brakes; ‘(2) © driving motors; (8). controller; (4) buzzers-~ a surprisingly serious source; (5) trolley contacting with the. overhead wires : (6)- convertors and gub-stations, signalling devices en route, and other minor ‘causes. — To the casual eye the simple buzzer in the trams-is an inoffensive installation,. . but investigation shows that the buzz of the buzzer is reflected in the interference in radio reception sets for hundreds of yards around. There is more than this nuisance for the tramways systems to consider, however, for the other points. mentioned have received the serious. attention of the department, ‘with the result that trams are dubbed ag eliminable nuis-

ance,. provided the controlling body is prepared to spend enotigh money-about :£5- on each vehicle. "Lhe most generous measure of co-operation .has been afforded the. department: in. Auckland, and other centres appear willing to, fol‘low their lead in the matter of ‘suppression of tramway interference. But, however. carefully the tramway concerns, throughout: the Dominion ‘cen sor" their -power jn ‘the, trams. themselves, there still remains the difficulty of eliminating the interference caused by, the existence of high-tension lines. THIS opens the wide question. of H.T. . interference generally, which intro-. duces more phases and suggests. still more difficulties for the department to ; ‘ solve. With the high-tension. power supply, the country listener-most en-‘ vied by his city brothers-is brought into the discussion. Many of -the city areas suffer in the same way as the country districts through which hightension cables carry their power supply. But what is the solution? : ‘Could the most autocratie department of the most autocratic Govern‘ment reasonably demand that ,the controllers of: this power . should equip anew their entire system-at-.a cost.of even tens of thousands ‘of pounds-for the benefit of a ifew hundred listeners? ‘There must be a limit called . somewhere, , and ‘that limit is intended -to.be within: the allocation -which the Post-and Tele‘graph Department allows for radio inspection. . Not that the Radio.Department of the P. and T. is responsible for the cost of suppression. ‘of. all interference, but if they "put their ‘foot down" as hard ‘as some listéners ‘would like, they would involve certain local bodies in. extensive expenditure which must eventually’ be met out of ratepayers’ pockets. The ‘whole question, therefore, narrows itself down to the point as to what is and. what is not culpable interference, and here, the department has powers and instructions which are being administered with discretion, Unfortunately, New Zealand ‘merchants of radio equipment have appeared to concentrate their attention upon providing sets which have the maxi--Iaum of interference-proof | qualifications. This is all very well, but there remains a field which allows plenty .of scope for economic: enterprise; the field * of marketing of interference: climinators, which are now the hope, the. only hope, of the: majority: of -city;listeners who have cause for complaint... Vacuum cleaners, hairdressers’ machines,.dental

equipment, machine shops, X-ray plants and diathermy clinics and a hundred other things all. have their share of blame in interference. xcept for the last, or possibly the last two named items of apparatus, there ig inexpensive and convenient equipment evolved for their elimination, but at the present time these simple means of elimination are not available to the average user of electric power which interferes with the purity of broadcast reception, HGH frequency. apparatus, such as is used in electro-medical diagnosis and treatment, has long been one of the most prolific sources of radio interference.: Unlike the majority of electrical devices which create interference in their immediate locality only,

certain types set up interference which destroys reception over a large area. Curiously enough, these systems, so serious in their effect, are perhaps the most difficult of. elimination. They are necessary for the health of patients. The redeeming features are that electro-medical apparatus is usually in action for only short periods of time and that there are not many of them. Canada has been one of the leading countries for experimentation ° ~ for eliminating interference, but even there it has been found that the present best method for. curing this fault is not often practicable. And it has been found, in diathermy apparatus. impracticable for medical purposes to use frequencies outside the broadcast band in a machine which is, in effeci, almost identical with the obsolete

spark transmitters. In New Zealand valuable research is being done to overcome the problem in its many phases, and in the course of time, with the expenditure of a-few pounds by power-users, it is certain that this department of radio know{edge will reach as high a standard of perfection as -those points :of -transwmission and reception which: we: have vrown to expect only in perfection.