RADIO NOTES

Rotorua Morning Post, Volume 2, Issue 234, 24 May 1932, Page 2

RADIO NOTES

"KATHODE."

By

Experimenters are anxiously awaiting the introduction of the new TripleTwin tube on the New Zealand market. This valve will he known as the Speed type 295. Receivers using the 295 in the output will not require any inter-stage coupling devises, therefore this saving in space will make possible midget sets of four or five valves. equal to present day console models. The characteristic curves of the tube show an almost straight frequency response from 30 to 50,000 eycles,' and the minimum distortion of the amplifier as a whole is about 5 per cent when the load impedence is equal to the plate impedence of the valve. The plate impedence is 4000ohms, therefore transformers ir. use to-day may be used with the 295. Some of the characteristics of the tube are. — Filament voltage, 2.5 volts, a.c. Filament current, 4 amps. Plate voltage (input section), 250v. Plate voltage (output section), 250v Plate impedence, 4000 ohms. Grid bias (input), 6 volts. Plate cuxrent, 50 m.a. * * * The world's record long distance telephony was established recently by means of a call from Christchurch to Buenos Aires, via Sydney and London. From Christchurch to the transmitting station in Wellington, the gap was bridged by ordinary telephone line. From Wellington to Sydney and from there to London, the Amalgamated Wireless service was used, the last link being the transAtlantic circuit between London and Buenos Aires, This contact was made in the nature of a test, and proved very successful. The voices, after traVelling over a distance of 19,000 miles, were quite distinet and audible without difficulty. * * * It frequently happens that when a pick-up is connected to a receiver, hum, howling, and other unwanted noises reseult. In most cases this may he cured by using armoured cable for the pick-up leads, the metal sheathing, of course, being earthed. A superhetrodyne receiver is not always adapted for pick-up use. This is not because of any inherent unsuitability of this type of circuit for the purpose, but because little low frequency ampification is usually employed. In most cases, the detector is coupled to a single 245, and the first audio stage is dispensed with. If the receiver employs a pentode amplifier, medium volume is obtainable from a pick-up. Contrary to popular opinion, television is NOT "just round the eorner." To use a prominent investigators remarks, "television may be round the eorner, but, oh! boy! what a corner." The writer has kept in touch with the progress of the science since Baird's first experiments, some years ago, and finds no hesitation in stating that television, as we picture it, "round the corner," will never be an accomplished fact. For instance, an operator in Rotorua will never be able to view the Melbourne Cup being run, in the same 'manner as he would be able to view a moving picture of the event. Static, fading and local interference would produce a blurred 'effect even if it were possible to transmit sufficient detail from outdoor subjects. The most successful wavelengths for television are in the region of five metres, but this part of the radio spectrum has a limited use. No objects, such as hills and high buildings must stand between transmitting and receiving aerials, otherwise little or no signal wll be received. Actually, this means that the transmitting aerial must be visible from the receiving aerial locaton. This alone will restrict the use of television. Then again, an extremely wide band of frequencies is required for producing pictures with clear detail, with the result that fewer stations would be able to operate without causing interference. Even if these difficulties were overcome, we would still require amplifiers of superexcellence, unheard of to-day. No, television has not arrived as a public utility. * * * Local conditions have been fair during the past week. The broadcast band has been more or less full of static, thongh occasional short periods have been excellent for reception of the YA stations. The Australians have been coming over with wonderful strength, though never entirely free from atmospherics. * * * Have you ever noticed the difference between the quality of music from KFI and the YA stations. The formed station has a grater depth of modulation and far surpasses the YA stations for tonal quality. "Kathode" has listened to most of the stations receivable in Rotorua and places 3AR Melbourne as first for tonal quality. KFI, Los Angles, is a close second, the YA stations being well down the - list. Next to KFI, the writer prefers 2FC and the 4QG, providing of course that the Australians are not suffering from distortion peculiar to long distance reception. These conclusions have not been drawn from experience with one particular receiver, but from results obtained from practically every brand of set used in Rotorua. * * * Conditions on short waves have been exceptionally bad during the last few days. On one or two occasions, good reception has been experienced for short periods, but in general conditions are much worse than for the corresponding period of last year.