RADIO NOTES

Rotorua Morning Post, Volume 1, Issue 20, 16 September 1931, Page 5

RADIO NOTES

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Conditions for reception have been excellent " during t'he past week, though static has been heavy occasionally. The Australian statiorfs have been eoming in well during the early evening, but fade out badly soon after 9 p.m. Polarity. To determine the polarity of a battery or eliminator, dip the "two terminals in water containing a few grains of salt. Violent bubbling willtake place on the negative terminal. One frequently "meets with the word polarity and it is interesting tp note the meaning Pf the term. The earth is taken as zero and points of pressure above it are said 'to be positive polarity, while points of pressure below that of the earth are xef erred to as negative polarity. W eather ' Changes. Impending changes in the weather always cause static, so that dflring early Spring, wlieri the weather is particulariy fiekle, static must be expected. When an electrical storm is approaching a hissing sound which gradually increases in intensity .will" be heard. This is caused by a stead'y electrical charge passing from the aerial circuit. to ground'. fyTaiiy attempts have beeii made to' invent" means for eliminating 'stafic, but so far none of them have beeh very suceessful, owing to the fact' that static impulses have no particular frequency and therefore cannot be 'elifriinated by any tuning means. Designing a Receiver. In 'designing a receiver three main points should be kept in view, viz.', selectivity, sensitivity and tone. To obtain selectivity, all faults tha.t produce excessive re'sistance must be ■ avoided, as r'esistaWce broadens tuning. The correct ariiount of capacity and inductance should be used, as capacity intro'duces resistance and too much of 'it would ruin 'selectivity. On the other hand, too high a value of will aiso ' produce resistance in the coil. All leads between circuits should be kept as short "as possible, particulariy those carryiiig radio frequency. Couplings between radio fr'equency circuits should be neither too close nor too loose. L^s a rule, loosening couplings will increase selectivity but if carried to far, poor sensitivity will result. A point in coupling is'reached where tjxe greatest transfer of power is' produeed. In securing sensitivity, the ratio between capacity and inductance together with coupliiig' must be watched. Radio frequency stages up'to'the point where noise level is "reached may be used, and correct voltages,together with appropriate valves, are essential. Good tone requires audi'o transformers of modern manufacture, appropriate valves and vPltages and a final stage of push-pull amplification. Matching of circuits is also essential and a good dynamic speakef is necessary. "B" Elimin3i.tors. Owners of "B" Eliminators and power packs frequently' complain of failing off of volu'me in their receivers, which is not remedied by a new set of valves. 'The rectifying fubes in eliminatdrs should alsb be-changed after long use. ' ' Confusing Term. The term. amateur, when .applied to transmittersj is somewhat confusing. Radio amateurs own and operate their own transmitting and receiving stations on wavelengths below those of the broadcast band. Amateurs should not be confused witk "novices," because . amateurs are highjy expert in their "avocation and their work in -the development of the radio art has been responsible for much of the advancement of this science. It was the amateur transmitters who experimented and demonstrated the usefulness,- of the. short wave bands, and it was the amateur who invented many of th'e modern improvements in radio. The term "amateur" comes from the fact that he is a person who follows the science because of a liking for it, and not for personal gain.