RADIO RECORD

Greymouth Evening Star, 10 August 1933, Page 3

RADIO RECORD

( Rv

“Reception” )

NOTES FOR LISTENERS-IN

RECEIVERS FOR CARS. NECESSARY FEATURES. Now that satisfactory devices for supplying cheaply the high voltage current necessary for the plate circuits of the receiver have been made available the use of receiving sets in motor cars is likely m increase lapidly (writes N. M. Goddard, 8.E., in the “Sydney Morning Herald”). Valve manufacturers have' for some time played their part by providing valves having filaments suitable for the standard car battery. These valves are generally similar to the a.c. type of valve, but have been usually designed to operate with lower plate voltages, since the plate current supply has until comparatively recently had to be taken from dry batteries, an expensive source' of energy.

There are many types of battery eliminating arrangements for cars, including motor generators and alternating current generators driven from a suitable part of the car engine and which supplies current to a power pack of the ordinary type. Another type of eliminator consists of a make and break or buzzer arrangement inserted in the primary of a transformer and fed from the ordinary car battery. This arrangement makes and breaks the primary circuit and produces what is virtually an alternating current, which is then, stepped up by the transformer and subsequently rectified by a valve or other rectifier and smoothed as in an ordinary a.c. circuit. The most important part of this type of arrangement is the interrupter, which makes and breaks the current in the primary. It requires careful design, construction, and adjustment if it is to produce satisfactory results and not consume too much power from the car battery, upon which the demand is usually of the order of five or six ’amps. In arriving at a suitable type for a motor car receiver, designers have had to take many points into consideration. In the first place, they had to revert to battery practice to a large extent. Then they had to make their equipment as light and as compact as possible, building it in sections so that the speaker, the set. the power supply arrangement and the tuning and volume controls could be mounted in places which were not normally required for the ordinary mechanism of the car or for the passengers. As a result of these restrictions, many ingenious arrangements of remotely controlled receivers have been made available, the controls being mounted on the steering column or some such place where they can be easily reached by the driver and the set and its power supply in some out-of-the-way position, such as behind the instrument board or on the bulkhead of the car.

A set. of this type is expected to give faithful reproduction since quality is, for the most part, the main feature of the ordinary receiver of today. Moreover, it has to be troublefree and simple in control and sufficiently sensitive and selective to give noise-free reception from a variety of stations under' what are sometimes rapidly and widely varying conditions as a. car which is travelling is constantly running into and out of comparatively dead areas. These requirements have meant that the superheterodyne circuit is desirable, while, due to the possibility of wide variations in the field strength of all stations, automatic volume control is practically a necessity. Careful shielding of all the parts is also essential because of the noise interference which would be produced by (he ignition gear of the engine or by the charging and discharging of the various parts of the vehicle- when it is in motion. The ignition system is from its very nature a. likely source of trouble, but its effects can be overcome by fitting as close as possible to each spark plug a. damping resistance, the value of which is not high enough to have any appreciable effect on the spark, but which is sufficient to kill any high-frequency oscillations set up. This, combined with shielding of the set itself, and armouring and the shielding of all cables leading to. and from it, is an effective cure. In other countries, the design of car receivers has reached such a stage that, comparatively cheap yet reliable and robust equipment of" a

variety of types can be obtained compactly assembled in easily attached cases and provided with all the- necessary cables and remote control apparatus to enable them to be installed in the vehicle in a few minutes. Many car manufacturers are including builtin aerials in the roof of the cars and providing places for the reception of the set and speaker as standard equipment.

PACIFIC WIRELESS NETWORK. A.W.A.’s ISLAND SERVICES. The British Islands in the Pacific scattered as they are over vast spaces of ocean, represent the extreme limit of worldly isolation, yet they are bound together by invisible links which permit communication with the same expeditiou as between the crowded cities of the world.

; Between the Solomon Islands, the Gilbert and Ellice Groups, the Fijis, I and the mainland of Australia J stretch an interlacing grid or net- ; work of wireless channels, connecting that great area, with the outside and each part with, the other. In the early days of radio a. fewsmall wireless stations were established by the British Government in Fiji and the surrounding islands. These were controlled and operated by the British Admiralty from its headquarters in London. Realising the development and importance of the various British island possessions in the Pacific and the enterprise manifested by other nations in establishing wireless stations on their island possessions in the Pacific, Mr Fisk, Managing Director of AAV.A., suggested to Mr L. S. Amery, then First Lord of the British Admiralty, that Amalgamated Wireless take over from the Imperial Government all the wireless stations in the Fijian group with the object of modernising and operating them as units of the Pacific network already operated by AAV.A. An agreement was completed between the Imperial Government and the Company in 1922 and to-day these stations are equipped in the most modern way. The speedy and accurate communication facilities thereby provided are greatly assisting the Fijian business interests. The most important of the Fijian wireless stations is at Suva, which collects and distributes wireless traffic to and from all islands in the North and South Pacific which have wireless communication. It handles overseas traffic with Great Britain and me Continent, and North and South America, via Sydney Radio and the Beam Wireless Service. Sydney Radio is also in communication with such important island centres as Samoa, the Friendly Islands, Gilbert and Ellice Islands. New Caledonia. New Hebrides and Honolulu. Communication is also maintained with the four other Fijian stations — Lahasa, Suva Savu, Taveuni and Lautoka.

An important, radio centre of the Pacific network is in the Mandated Territory of New; Guinea, where the Company’s chief station is located at Bita. Paka, near Rabaul, on the island of Now Britain. This modern station maintains direct radio communication with Sydney and with the following stations: Aitape and Madang, New Guinea, Manus, Admiralty Islands, Kavieng, New Ireland, Kieta, Bougainville Island, and Wan and Salamoa on the New Guinea goldfields. It also communicates with the Gilbert and Ellice, Solomon, and Santa. Cruz Islands. At Port Moresby, in Papua, is another unit of the Pacific network. From here communication is affected with Samara!, in Papua, with Thursday Island. and with Cooktokn and Townsville in Australia.

The principal Australian wireless stations handling traffic between Australia and the Pacific are located at Sydney, Brisbane, and Townsville. These in turn are intermediary stations between the Pacific and the Beam Wireless Service connecting Australia with Great Britain, the Continent, and North and South America. Thus the island resident is able to communicate by wireless with any part of the world, ft. will thus be seen that the ideal of a British network in the Pacific, is in course of realisation and that Australia is - fast becoming the important wireless clearing centre of Pacific communications.

DETECTION PROGRESS. Every listener knows that the process of detection is essentially one of rectification. Both the crystal detector and the diode valve detector_ operate- as simple half-wave rectifiers, while in the three-electrode detector, a certain measure of amplification is also obtained. Thus the leaky grid detector acts as a half-wave rectifier plus a, low-frequency amplifier, while the anode bend detector is, in effect, a, high-frequency amplifier followed by a half-wave- rectifier.

With the diode, rectification is practically perfect, but so far this system has not achieved any great measure of popularity, because it necessitates an additional valve, and thus adds to the cost of the receiver.

Two diodes, operating in push-pull to give full-wave rectification, form an almost ideal system of detection, pnt there is still the feeling that a certain amount of voltage amplification should be provided in the detector stage.

The solution of the problem will be in special valves in which one or more diode rectifying elements will be combined with an amplifying electrode svstem. Several variants are possible—single diode combined with either triode or tetrode, and double diode combined with a triode or tetrode.

In the double-diode-triode, which represents possibly (he most. useful combination, a single ’cathode- is employed. Two small anodes serve for the full-wave rectifying portion, and the rectified output is then passed to the control grid of (he triode portion, which has its own anode and operates as an audio-frequency amplifier. Thus, detection and amplification are kept entirely separate within the one bulb, the- triode portion of the valve being electrically screened from the rectifying element to prevent unwanted coupling. The same, type of valve can be employed in other ways. For example, one of the diode anodes can be used for half-wave rectification, while the other serves for introducing automatic volume control.

PAPER CONDENSERS. A small point with regard to paper condensers of high capacity may be responsible for uncertainty when a stock of existing components is to bo used in building a new receiver. The non-inductive condenser has only been manufactured in large quantities during the last few years. Condensers of earlier vintage will probably be inductive, and unless they can be guaranteed as free from this property, there may be a natural hesitation to use them, even though they may be rated to withstand the voltages existing in the receiver. These doubts may- be set at. vest by saying that there is very little risk of trouble through using inductive condensers in any position -except where I-T.F. currents are to 'bo dealt with. Accordingly, old condensers may be employed in L.F. circuits for by-pass and decoupling purposes, and also for smoothing, but they should not be inserted in the anode, grid, or screening grid circuits of the I-T.F. amplifier.

With regard to the detector anode circuit, where both H.F. and L.F. currents are handled, the position is not quite so clearly defined, but as a general rule the use of inductive condensers is not likely to do serious harm. Any paper condenser of high capacity, will almost invariably be on the “dead” side of any H.F. filter that may be included in the circuit. . REGULATING- NEWS BROADCAST Strict regulations governing the broadcasting of news over Canadian radio stations have been enacted and put into effect by the Canadian Radio Commission with a. view to protecting the rights of newspapers in their own product and to the assurance of accuracy and authority in news bulletins thus transmitted.

The new regulations ' were drawn up following negotiations with The Canadian Press, the co-operative news collecting and distributing agency of the Dominion, and are as follows:

“Canadian radio broadcasting stations shall not. transmit any news or information of any kind published in any newspaper or obtained, collected, collated or co-ordinated hy any news-

paper or association of newspapers or any news agency or service except the following: “Such news bulletins as are released regularly from the various bureaux of The Canadian Press for the express use of broadcasting stations in Canada.

“Local news under arrangements to be made by each station individually with its local newspaper or newspapers, or such news as it may collect through its own employees or through such collection agency or agencies as may be employed by the said station.

“Newspapers broadcasting false or misleading news shall bed prohibited from further broadcasting unless extenuating circumstances can be shown.

“The broadcasting of editorial opinions of a. controversial nature is prohibited.”

Regulations in respect to programmes prohibit any reference to pi ice in commercially sponsored periods. Unless special permission is given the amount of advertising matter Jn a programme is limited to five per cent of a. period. Programmes must be filed weekly with the Commission, and sustaining programmes originating outside Canada must give priority, at the request of the Commission. to programmes of national interest originating in this country.

SHELLAC FOR CONES. For those who have a. home-ffiade brown paper cone speaker, this wrinkle is well worth trying. All that is needed is a stiff mixture of shellac, a brush and a fire. First turn the outer edge of the cone over tm eighth or a quarter of an inch all lound. This can be glued or stitched. Then give the cone a liberal coating of shellac on either side. When dry, insert a piece of wire through centre hole of cone, and hold in front of fire till shellac melts. (This causes it to soak through the paper). It should then be left about ten minutes to set, after-which it can be reassembled, and will give a clearness equal to many of the best commercial speakers. The idea of turning the edge over is to act as a stiffener.