For Prospects and Recruits

Radio Record, Volume I, Issue 16, 4 November 1927, Page 16

For Prospects and Recruits

By

M.I.R.

E.

This column is conducted by a member of the Institute of Radio Engineers, with the purpose of giving prospective buyers informati on of value.

.Following on the remarks made 10 these columns in our last week’s issue concerning interfering electrical noises" experienced in the reception of broadcast signals, it is desired_to deal with some aspects of the situation with respect to the reception of signals from distant stations ‘The electrical noises referred to were stated to originate either in the earth’s crust or atmosphere due to the flow of electrical curcents consequent on natural causes, and generally known as "static," or were caused by man in the reticulation of energy in the form of power for lighting, heating, and other purposes — "Distant" is naturally purely a relative term. A medium-powered transmitter 400 miles away is distant for a two-valve set-very distant, as a matter of fact. On the others hand, to the possession of a six-yalve set the same station is normal loudspeaker reception. From the point of view of interfering noises, the owner of the six-valve set is going to bring more trouble than the owner of the two-valve set, because he has four more valves to bring up the interfering noises to an annoying strength Of course, for normal reception of relatively close-by stations, the six-valyer is on clover, because he merely goes and switches on his set, gives a dial.or two a casual twirl, and then sits hack to reliable clear-cut reguits. whereas our two-valve friend probably starts off with '’phones, and after careful adjustment and holding of breath in spasms, transfers more or less satisfactory signals to his speaker: and at the least sign of fading is forced to again plug in his "phones. THE FACTOR OF CONDITIONS. When chasing stations reckoned as distant to a mualti-valye set carrying as matiy as, sav, six yalves, the same conditions commence to apply Providing interfering noises are not too great, *phiones may be used to search for signs of the desired station, and then the apeaker plugged in after the receiver has been adjusted satisfactorily. As has been explained previously, in these colimns the sensitivencss of receiving conditions vary very creatly, according to the localitv. Sensitivencss of reception is invariable found to apply to stations whose signals come from all directions, but in some instances it is found that a locality is wltra-receptive to signals coming from one or two directions, and is normal, or even subwormal, with respect to other directions.

Sensitiveness of reception represents efficiency of recention naturally, but this is more readily appreciated when it is understood that distant reception merely amounts to an equation having two factors, and may be represented as follows. Successful reception equals the signal strength subtracted by the interfering effects. If there were no interfermy effects, then given the requisite number of valves, any station in the world could be tuned in, and in those localities where reception was not up to standard, more yalves would have to be used than in a locality where reception was normal, or above normal... The number of valves used does not alter the equation men tioned because both signals and interference receive amplification while passing through the valve system, and the relation of signals to noises remains unaltered. (Actually noises usually receive slightly more amplification for technical reasons.) . The modern general-purpose valve has an energy amplification of a certein yalne when used in an orthodox design or receiver. There are many brands of valves, and many more brands and designs of receivers. There are ajl classes of performances put up by combinations of valves and receiyers. A poor design of recciver giving a performance with poor valyes, may perform in a more cheerful fashion when good valves are used, and an excellent design of receiver may be quite ruined by poor valves. In spite of such a _ statement it is possible to state’ that given a receiver of recognised make fitted with valves also of a recognised make, a standard of reception may be arrived at for any style of réceiver carrying so many yvalyes, Thtre are a dozen different designs in receivers on the New Zealand market which, if lined up together under identical battery power, would give a performance which would be practically equal so far as picking-up propensities are concerned, It can be stated quite de-

‘finitely that any style of receiver haying the same number of valves which showed a greater signal strength could only do it at the expense of sacrifice of tone or simplicity of control. FOUNDATIONS MUST BE: RIGHT. These remarks have been made with the object of showing that there is a foundation for the statement that, given normal receiving conditions, a medium aerial of thirty or forty feet high, a six-valye set can be expected to give a performance which should include all the year round reception of Australian and New Zealand stations anywhere in New Zealand and should also bring in American and Japanese stations under good conditions of static interference. That sentence "good conditions of static interference" is the usual fly in the ointment. These remarks are being purposely made pessimistic, so far as real distant reception is concerned, in order to try and dispel some of the illusions existing in the minds of many people to-day. . The prospective buyer of a multivalye set who has had his fancy tickled by the idea of sitting back with his feet on the mantelpiece every night and being entertained by the subjects of Uncle Sam and the Mikado of Japan must alter his perspective vastly or he grievously disappointed even after he has purchased the most expensive outfit obtainable in the country. Admittedly there are hundreds of sets in New Zealand to-day which are regularly getting American programmes, but there are hundreds more which don’t and never will until they shift to a more receptive locality. There are dealers who guarantee all sorts of performances for their equipments in their advertisements If taxed with the palpable impossibility of their equipments coming up to such a standard they will cheerfully tell the same

story that Adam did about Eve and the apple-the other fellow started it. If John Citizen goes to number one dealer and is told that his set will get America, and dealer number two hesitates, many John Citizens who don’t know -better get suspicious of number two dealer's goods. ‘The writer of this article would advise John Citizen to give dealer number one a wide berth in future, nnless his statement of American reception is well qualified by a warning that the occasions on which he will actually get such results are more seldom than numerous, and are dependent on conditions. MODEST CLAIMS BEST, Take notice of the dealer who is modest in his claims regarding distance performance, Lut who lays himself out to give all the information he possibly can to assist towards a realisation of the factors determining successful distance getting, and who, if necessary, is prepared to refer you to individuals owling equipments of his design, and who are likely to have receiving conditions comparable with your own, in order that yon may get first-hand and unbiased information. In passing, it is worth while mentioning that when dealing with the radio trade, always look for frank: ness, Treat with immediate sus: Picion any apparently extravagant Claims, As has been said before in these columns, trust nobody but the manufacturer, distributor, or authorised agent for information or advice regarding any particular make of machine. Yxtravagant claims do not live up with thie guarantee of satisfaction which should always be forthcoming as one of the terms of sale. . Now, to view the from the point of view of the dealer, it is best to take the analogy of that very uscful vehicle, the motor-car, The

radio distance-getter is akin to the speed fiend. ‘The maker of a car will tune it up and demonstrate its performance at eighty miles per hour. He picks his track, however, naturally, and he doesn’t attempt the test after there has been a week’s heavy rain and the track is dangerous. Furthermore, he doesn’t guarantee to keep the car tuned up to the necessary pitch to enable the driver to get such a speed every time the accelerator is pushed hard down. Of course, if the purchaser of the car is prepared to pay for tuning periodically it is a different matter. However, this is more or less beside the point, the main consideration being the fact that a car which has a reserve speed of eighty miles per hour is only of real use to the owner on a race track or on special roads, so far as its reaching-out propensities are concerned. ‘The power which is able to push the car to such a speed is, nevertheless, immensely valuable in hill-climbing, etc., at reasonable speeds. So to return to the multi-valve radio set. Given clear conditions it can be pushed to the limit, but if there is. static interference or if there is anearby broadcast station transmitting on a wavelength near to that of the distant station it is required to receive, so inevitably will the* distance range be closed in, just as the driver of the car is compelled to slow up because of cross roads or pot-holes. As was stated at the beginning of this article, the multi-valye set will give great reliability when receiving nearby and will: give what is most important of all, permanent satisfaction becanse of adjustability to all conditions. In conclusion, the writer cannot resist repeating another previous remark, and that is that New Zealand listeners have learned to run before they attempted to crawl, because of the almost universal rush after the distance, which does not always cause the enchantmert to materialise, when enchantment is to he had right at home, by listening to vhe local N.Z. stations, and thus dodging the bughears of radio in the shape of static and fading, etc. eee