RADIO AND ITS RECEIVERS

Sun (Auckland), Volume I, Issue 233, 21 December 1927, Page 14

RADIO AND ITS RECEIVERS

Conducted for THE SUN by

C. M. Taylor, B.Sc., M.I.R.E.

AUCKLAND’S RADIO CHRISTMAS The Auckland dealers, in conjunction with the assistance of the Radio Broadcasting Company, have made very full arrangements for the purpose of bringing before the public that ra<jio has definitely outgrown the toy and com-plicated-apparatus stage, and is now listed among the necesisties of the modern home. At Christmas time, when one's thoughts turn to gifts, radio offers a field which is unique in that there is something which will give pleasure to everybody. For example, a set for Mum and Dad, •an amplifier and speaker for the crystal set, an eliminator, or charger, an extra pair of phones are all general gifts. For the man keen on construction, or the youth building his own set, the choice of componets is legion, a new valve opens up many unexplored fields, a new condenser or transformer means the fulfilment of desires for adding that extra stage of amplification. A new set of batteries is always most acceptable, and there are many neat and novel little accessories which add to the interest of radio, such as a volt-meter for testing batteries or a hydrometer for keeping the accumulator up to concert pitch. EXTENDED PROGRAMMES FROM IYA

The Broadcasting Company is seeking to aid the dealers and contribute to the holiday spirit by extending its sessions very materially. This week, transmissions are starting at noon instead of 3 p.m., and next week the station will be transmitting from 8 a.m. till 10 p.m. These extended sessions are only an indication of what must come in the near future to bring our broadcasting service into line with that of other countries, and the rapidly-in-creasing number of licences should soon make this possible.

INTERESTING STUDY

RADIO IN AUSTRALIA A FEW OBSERVATIONS To a New Zealander radio conditions in Australia form an interesting study. The first thing that strikes the visitor is the excellence of the service rendered by the broadcasting station. Starting at 7 a.m. with the latest Press news that main stations are on the air throughout the day with small intervals, weather reports, stock markets, racing news, and musical items are given, the stations continuing until 11 p.m. In Sydney alone there are five stations operating, and with a selective receiver almost any type of programme can be hkd. The programmes of the larger stations such as 2FC and 2BL are in general excellent, and are given with a very small interval between items. It is true that occasionally long rather drawn-out talks are given, but generally there are one or more stations giving musical items so that the listener can finijj something to suit him should he not wish to hear the lectures. During the. time the writer was in Sydney a considerable number of sporting events was broadcast. In each case however the efforts were very poor, due chiefly to the lack of knowledge of the describer. The New Zealand Broadcasting Company is fortunate in having Mr. Alladyce on its staff, his descriptions of games and races being so much better than that of the Australian announcers that a comparison would be odious. BROADCAST RECEIVERS A noticeable feature of the radio trade in Australia is the absence of American receivers in any quantity' such machines as Bremer Tully, Freed Eismann, Fada, being only seen to a limited extent. The reason for this is the high customs duty imposed on foreign machines, making the cost of an imported receiver approximately 75 per cent. As an v example a popular five-valve receiver which sells in New Zealand for £46, is sold for £75 in Australia. The effect of this high tariff has of course been to stimulate tocal production, and many of the receivers which are offered to the public are of poor construction and design, and have an “amateurish” appearance. Of course there are a number of excellent receivers made in Australia. Some of the receivers which were examined were of a. design which would be prohibited here, and the general construction of tho receivers was inferior to many a New Zealand home-built receiver. HOME-BUILT RECEIVERS As regards radio components a large proportion of these is made in Australia by such firms as Emmco, Signal, etc., and there are quite as good as those imported from America. The Australian set builder, however, is satisfied with far less than his New Zealand brother. His main source of information for circuits is the daily paper. The writer was rather amused to find that a number of his circuits which have appeared in THE SUN had been pirated by Australian papers in some instances with no acknowledgment. In one case a radio salesman asked the writer if he had ever seen a circuit called the RBD, which, he said, had been originated by an Australian. In a city such as Sydney a selective receiver is of first consideration, yet few machines which are offered there are selective as the Browning Drake. With five broadcasting stations in operation a superheterodyne is really the only type of machine to use, and the writer’s suitcase Radiola had no difficulty in getting any outside station through the local stations. Station ~ya, Wellington, came in nearly every evening, but the strength was most disappointing, especially as the power or this station is considerably in excess of any Australian station. The writer was told that for the first few days after the station opened 2YA cam” through with great strength, but since then the strength has fallen considerably, and the station fades very frequently. The remaining New Zealand stations are very weak. AMATEUR TRANSMITTERS Amateur transmitting enthusiasts are handicapped to about the same extent as those in New Zealand, particularly as to the transmission of messages, and there is always a telegraph official listening to what is being sent out. In spite of this the transmitting men are doing good work, and there is scarcely a country in which their signals have not been received. A feature of Australian broadcasting is the relaying of American and English short-wave transmissions, and some very effective work has been done by 2FC, in conjunction with the Amalgamated Wireless Company.

There are many interesting processes m modern broadcasting which because of their smooth working attract little attention.

The methods used to convey “outside broadcasts" to the studio are in themselves fairly simple, but the apparatus used and its proper operations call for nice technique. Broadcasting from a point distant from the studio involves the use of a “line amplifier,” an instrument which,

with its associated microphone, is used to pick up the entertainment, amplify it to a suitable degree, and transfer it to the telephone lines, which in turn convey the transmission to the studio. Except in very long distance broadcasts, where trunk lines are involved, two lines are used —one for “monitoring,” enabling conversation between the operators at either end, while the transmission is in progress, and one for the transmission itself. The microphone used for outside work is the same as that used in the studio, though perhaps housed in a lighter and more portable casing. The pedestal on which it stands is very light also, for the apparatus has frequently to be conveyed by hand from poijit to point. The amplifier itself calls for very special design. We are all familiar with the microphonic qualities of valves in an ordinary receiving set and the ringing noises created by them. Imagine the noise from a receiver magnified a thousand times and some slight idea will be gained of what would happen if the valves in a line amplifier were even slightly microphonic. The noise might even submerge the transmission proper, and so elaborate precautions must be taken. The valves themselves are designed specially to be very quiet in operation, while carefully mounted sockets add further protection from mechanical vibration. Batteries and connections must be kept in .perfect order always for the energy from the line amplifier is passed through five or six further stages of amplification before being fed to the giant transmitting equipment at the broadcasting station. Because of this and more obvious reasons a line amplifier must give absolutely distortionless amplification. As a rule transformer coupling is used between valves as the energy from a broadcasting microphone is very small and must be amplified considerably. The line amplifier brings the microphone energy to good headphone strength which is sufficient to send over the telephone lines to the studio. The variety of modern broadcasting calls for a large number of line amplifiers all of which must be kept constantly in perfect order. Batteries have to be watched carefully to see that voltage is well up to standard. Usually accumulators are used to feed the valve filaments while dry cell batteries are used for the plate supply. Spare valves are provided in the amplifiers and every emergency is provided for.

The placing of microphones in outside work calls for skill and experience as there is usually no time for experiment, and once placed a microphone must remain in that position. In the open air the effect of wind must be kept at a minimum for the varying pressure of air on the sensitive microphone causes a great deal of noise and at times even paralyses the instrument temporarily. An example of wind effect was provided at the recent Armistice Day ceremonies when owing to the unavoidably bad position of the microphone it was subject to the full pressure of a high wind. The outside operator having placed his microphone immediately gets into telephonic communication with the studio and asks for a test. The studio operator listens to the characteristic noises—the actual performance not having started —and from his experience judges of its volume. RELIABILITY GREAT

He then instructs the outside man to increase or decrease volume, and comments on the condition of the telephone line or on any foreign noises. The test ended, the studio operator can switch in the outside broadcast at exactly the right moment and so preserve the continuity of the programme. All switching of this nature is carried out without “clicks,” and a studio will be “faded out” as the outside item is brought in. The recent vogue of country broadcasts called for considerable organisation and though the outside apparatus travelled perhaps hundreds of miles, no hitch occurred owing to faulty instruments —a tribute to the reliability of modern equipment. A most important feature of outside broadcasts is the condition of the telephone lines, which, if imperfect, would nullify the most elaborate precautions. Here again tribute must be paid to the sister science, for although telephone talks on coutnry lines are at times exasperating, it rarely happens that broadcasting is marred by noisy lines. NEW APPARATUS

THE SUN has had on test a British portable set, which is the last word in portable design, for loud-speaker strength within a radius of 250 miles of a main station. The set gave excellent results on Auckland, and quiet loud-speaker on Wellington at 8 *p.m. Sidey time. Resistance coupling is mainly used on account of the lightness. The aerial is enclosed in the set, which has five low consumption valves worked by a 2 volt accumulator of non-spillable type. Single-dial control and provision for external aerial and loud-speakes, in addition to the selfcontained loop and speaker, make up a very complete equipment. The set is the Burndept Portable.

Where extreme selectivity and distance getting 1 are the features, it would be hard to beat the Bremer-Tuly Counter Phase 8. Situated quite close to IYA, 2BL comes in without any interference from the local station, this selectivity being obtained by means of a special rejector stage which is incorporated in the design. As a tribute to its power and selectivity THE SUN uses this set to obtain news from the other New Zealand stations during daylight, and while IYA is on the air. VOLTMETER In order to increase the range of a voltmeter, it is necessary to connect a resistance of suitable value in series. An ordinary potentiometer of the wirewound type is very suitable for this purpose, and is a component which most amateurs possess. By this means it is possible to use a low range filament voltmeter for measuring the voltage of the H.T. battery, the correct value of resistance being found by a series of experiments with batteries of known voltage, or by comparison with another instrument. DRY BATTERY

The life of a H.T. battery constructed with flash lamp battery units will be greatly extended if the batteries are treated in the following manner before assembly: The paper cover of each battery is pierced in several places in the space between the cells. Each battery is then dipped in a bath of molten paraffin wax (not too hot) until fully saturated. Not only will the wax improve the insulation and prevent leakage currents from flowing between different parts of the battery, but should one of the zinc containers become eaten away toward the end of the useful life of the battery the trouble will be isolated by the wax, and prevented from spreading to other cells.