RADIO

Southland Times, Issue 21101, 5 June 1930, Page 13

RADIO

IYA BROADCASTING CHOIR

ENJOYABLE PERFORMANCE.

Since its inception in June of last year the IYA Broadcasting Choir, which was formed on the recommendation of the IYA Musical and Dramatic Committees, has provided a number of enjoyable and varied programmes, says the N.Z. . Herald. The choir, which is conducted by Mr L. Barnes, station director, gave its first performance last August when it numbered 30 voices. There are now 40 members comprising equal numbers of sopranos, contraltos, tenors and basses. Rehearsals are held at the station every Monday evening, prior to which \a half hour of instruction is given by the conductor. The members have all been carefully selected, their average age being below that of the average choir. The soloists at the concerts are all members of the choir. Mr Cyril Towsey is the pianist.

Concerts given by the choir to date are as follows.“ The May Queen” (Sterndale Bennett), “The Banner of St. George," “Songs From the Bavarian Highlands” (Elgar), the Christmas music from the “Messiah” (Handel), and “The Rebel Maid” (Montague-Phillips). The majority of the choir attended the station from eleven o'clock until midnight last Christmas Eve and rendered Christmas carols. THE SILENT NIGHT WAS THERE A PROMISE? The “Radio Record,” in an editorial, practically contradicts a statement put into circulation that a promise was given that the silent night would be abandoned this year by 2YA, and also that the hours of service would be extended. It is unable to recall any promise of this nature having been given by anyone in authority. It does, however, recall printing in December an article forecasting the abolition of the silent night as the next major concession to be granted to listeners. “Looking back on the advances made over the last twelve months, we strongly hope that the incoming twelve will see the abandonment of the silent night.” And the Record desires its memory to be refreshed.”

In the Evening Ppst of 9th January the following appeared:— “A definite promise has been made by Mr A. Harris that the 1 silent nights ’ will be abolished at all the YA stations next winter. It is intended that subsequently (though there is no indication of the probable date of the change) a midday session, from noon, till 2 p.m., will be instituted as a daily feature, and later still morning sessions will be added. The projected abolition of the silent nights will be a very welcome, change. It has been repeatedly advocated in this column as an important factor in reducing the prevalence of interference by oscillating receivers, and the fact that the Broadcasting Company is at last in a position to abolish a fault which can only have been justified on strong economic grounds is a matter for general congratulation.” It is admittedly unfortunate that after this lapse of time it is not possible to produce the original evidence (published in an exchange), on which the assertion quoted was based. It must be apparent that such a statement would not have been published, and reprinted in other papers and left entirely uncontradicted until now, if such original evidence had not existed; and the present writer believes that the state-' ment was correct. Whether such a promise was actually made or not, the fact remains that it is high time the broadcasting stations abandoned their distinction,.of being the only prominent broadcasting stations in the English-speaking world to require a weekly rest. There is a very wide demand for the abolition of this absurd silence, which confers no benefit on anybody. One argument in its favour is that it enables people with valve sets to tune in stations which on other nights are blanketed by the local station; but it is common knowledge that sets which are of such a kind that they are so handicapped are the cause of continual intereference on the silent night, and that nobody then has good reception of ■ anything. Apart from the matter of the extra cost to the company, there is not a single valid excuse for the continuance of the silent night.. In view of the fact, that the number of licenses is annually inci easing the financial argument has lost much of its validity.

AMPLIFIER DISTORTION

BIAS AND OVERLOADING,

If a milli-ammeter is inserted in the plate circuit of the valve to be used and the value of plate current measured for a series of valves of grid voltage, these can be graphed, stated Mr J. C. Stewart in a lecture given before the Auckland Radio Society, says the Herald. The curve obtained is known as a characteristic. _ Its shape is made up of a straight portion, curving toward zero current. At the top portion the curve again becomes horizontal at saturation, but this should never be reached even in testing. If the grid current is measured with a micro-ammeter a similar curve is obtained. This shows that when the grid becomes sufficiently positive the resistance gnd-hla-ment drops from the value of megohms to perhaps a few thousand ohms, lhe significance of this will appear later. For an amplifier to generate a voltage of wave-form the exact pattern of that of the voltage supplied, the characteristic must be straight over all the portion employed. This can be seen, for the voltage output is generated by the fall of voltage over a resistance, choke, etc., and in all cases is proportional to the A.C. component of the current. If now this has a different waveform from the impressed voltage then there will be distortion. If the characteristic has a bend at one end, slope decreasing say, then when the grid voltage has the appropriate values, the plate current will not. fall off as it would with a straight characteristic. .There will be some D.C. generated, and also as may be shown, some A.C. of higher frequencies (harmonics). This produces a distortion. The D.C. is changing and produces clicks if sufficiently rapid, while the harmonics alter the tone of the note. The magnitude of this distortion grows very rapidly with the loudness. In the extreme case where the effect is used for the purposes of a detector, the second harmonic is 25 per cent, the strength of the first harmonic, or fundamental, if a 100 per cent, modulated carrier is being “detected!" _ _ If now the grid swings to positive then the grid equivalent resistance drops to quite small values. This shortens the input transformer secondary, varying the load, and hence cutting down considerably the voltage really applied to the grid. This produces D.C. in the opposite direction to the other effect, by chopping off the peaks on one side of the wave.

When a valve is overloaded the gridswing goes beyond these two points where distortion stars. The effects may cancel for a certain loudness, but cannot cancel for all intensities. The most general way of tesing this effect .is to place a D.C. milliammeter in the plate circuit. If the meter gives a "kick” upwards with a loud note then the bias is too negative. If a “kick’’ sometimes up and sometimes down, is observed then the valve is overloaded and no adjustment of bias is any use. A largerpower valve is needed. A micro-ammeter in the grid circuit is used to indicate that the grid is becoming too positive.

The latest figures to hand show that the total number of licenses issued in Canada is 375,068, as compared with 296,926 last year.

SETS OF THE FUTURE DROP IN PRICES PREDICTED. GROWTH OF REDIFFUSION. ■ADAPTABLE FOR “TALKIES.” During the past few years receiver design has advanced until further progress seems impossible. Captain P. P. Eckersley, the well-known English radio expert, however, has some novel ideas for the future. Captain Eckersley writes as follows: — It is rather interesting to discuss what type of set will survive during the next decade. To-day we have the following points, as the merits and demerits of each type. The great merit of the portable is that it is so portable. There are, however, batteries to charge, there is cramped design, and quality which, while sufficient for certain purposes, can and ought to be surpassed by mains-operated and outsideaerial models. The great merit of an A.C. transportable, i.e., a portable set that works off the mains, is that it is portable, but the degree of its useful range is the limit of where one finds alternating-current mains. The Aerial and Earth Receiver. The merit of the aerial and earth set is that it can be extremely cheap, for as the aerial increases in size the field strength gets stronger. Design need not be compact, and one can do with few valves and simple circuits what the portable and the transportable have to do with many valves and complicated circuits. The aerial-earth set, if the aerial has to be pretty large to make the set cheap, suffers from lack of selectivity, does not always give the owner a great range of programmes, and has to sit in one place all its life. There is an obvious future for the combined radio and gramophone set. I think one of the points which stands out is that with the variability of conditions and the variability of desires we shall not see one type alone oust all the rest. I class future' sets, therefore, as follows: First, the portable set is bound to survive practically in its present form. A high-tension battery that has a very long life, even with a high discharge rate, and also cold emission so that the lowtension battery dies is wanted. The transportable set will survive in twq, forms, first for reaching out, second for only the local station. The former will be more expensive than the latter. People will put these transportable sets into a gramophone, when you get the combined instrument and have ’'local stations and gramophone or distant and local stations and gramophone. Will the Aerial Finally Die? The aerial and earth set will, in my opinion, finally die. One cannot foresee that the future will be satisfied with the trouble incident to the installation of aerials and earth. The - greatest seller today is the portable, only because it is selfcontained and complete. Headphones will, of course die, except for very poor people. A gradual cheapening process in design and manufacture will, I think, bring about all the changes I have indicated. How it will be done will be another story. But what is going to happen about this rediffusion business Rediffusion, where it is adopted, means the death of the individual receiver. Thus you take a given town, which we will call Zonk, where individual reception conditions are poor. We postulate that Zonk has a weakish field strength, a good deal of interruption, crowded houses with little room for aerials and a poorish population. Suppose we now install a good wireless receiver outside Zonk, away from trains and interference. This will be fitted with special directional aerials and every device known»j.to get. perfect quality and freedom from interruption. A Community Super-Set. Then wires are run from this receiver all over the town to subscribers, and all the listener has to do when he wants to listen is to plug a loud speaker into a hole in the wall. Properly rigged up there are two holes, one for one programme, and one for the other.. This can be done for sums like 2/6 and 5/- a freek, and cover the cost on reasonable numbers. We see at once that the consumer docs not gain much in actual cost for the service. He also loses the possibility of reaching out and is limited sometimes to one programme, and sometimes to a choice of two. He gains enormously, although, in that he gets a no-trouble service, has no serious capital cost, and is not in fear of obsolescence. In my own mind, the future will see the portable, transportable, mobile radio gramophone, adn rediffusion, all satisfying the needs of different classes of individuals. I am sure in my lifetime I shall see the practical elimination of the outside aerial and earth. I shall see programmes diffused not only by wireless but through the mains. I shall see the cost of a radio gramophone of first-class quality down to £lO to £l5 and such simple sets as transportables down to £5 to £7. The sets will be adapted as attachments for home “talkies,” and many more people will use their gramophones for their favourite musical pieces because we shall have the continuous record storing a whole opera or symphony. CORRECT USE OF COILS There are good and bad coils,. and there are good coils which may behave like bad ones if they are not used under proper conditions. For example, a coil may be placed too close to a metal surface, with the result that serious losses may be introduced and these losses have eventually to be made up. On the other hand, the change in the effective inductance of a cod, brought about by the presence of a metal shield, may mean simply that a different tuning capacitv is necessary for a particular wave-length. The high-frequency resistance of a coil is a point which needs careful consideration, and, although it is impossible to do away with the H.F. resistance altogether, its value should be kept as low as possible. The influence of resistance and corresponding damping is. particularly ■ noticeable when considering the question of selectivity, and here the difference between a circuit with a good coil, operating under efficient conditions, and a circuit with a bad coil or with a coil operating under inefficient conditions is very noticeable. RADIO IN AMERICA The following figures show the remarkableable growth of radio broadcasting in the United States during the seven years it has been in vogue. The number of licensed broadcasting stations is just over 600, and the equipment, of the same is valued at about five million pounds. The staffs of these broadcasting stations numbers about 8000 persons. About £50,000,000 is invested in the manufacture and distribution of radio sets, while in the radio factories about 100,000 people are engaged, receiving about £50,000,000 a year in salaries. The radio sales last year amounted to about £150,000,000, or about £3,000,000 a week throughout the year, while during the whole of - the past six years the sales of radio apparatus have totalled about £500,000,000. The radio sales in 1929 were just about ten times those in 1922. During 1929 about £3,000,000 was spent in the United States on the broadcastiing of music alone.

Band music is one of the most popular forms of radio entertainment. It is the intention of’IYA to arrange for three band recitals a month. The Auckland Waterside Workers’ Silver Band has not been "on the air” for about two years, and regular broadcasts by this band' are to be included, if possible, in the scheme.