RADIO AND ITS RECEIVERS

Sun (Auckland), Volume I, Issue 179, 19 October 1927, Page 14

RADIO AND ITS RECEIVERS

Conducted for THE SUN by

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

SHORT WAVE STATIONS

The principal short-wave stations are as follow: — 2XAD.—Schenectady, U.S.A., 20 metres. 2NM.—Chaterham. England, 23 and 33 metres. 2XAG. Schenectady, U.S.A., 26.92 metres. PCJJ. —Holland, 30.2 metres. 2XAF. Schenectady, U.S.A., 32.79 metres. RFN.—Russia, 45 metres. VVLW. —Cincinnati, U.S.A., 52 metres. KDKA.—Pittsburgh, U.S.A., 63 metres. WGY. —Schenectady, U.S.A., 89 metres. SWF.—Perth Western Australia, 100 metres.

SPORTING RELAYS Great disappointment was generally felt at the refusal of the trotting i authorities to permit the broadcasting : oi the last meeting in Auckland. One ; does not hear of any definite reason ! for this step, and one can only guess j that the reason is that people are stay- j I ing at home to follow the sport of 1 ! kings. To the racing enthusiast this ! can hardly be possible; to the people to whom a race meeting is a purely social event the relay cannot fill the gap; and the wide circle of people whose interest in race meetings is being stimulated by radio the loss of the relay will have a detrimental effect. In fact, everj'one regrets the passing ! of a most interesting transmission ! -which, with the quality of the announcing from the course in the last | transmissions, was bidding well to be j the most popular of the daylight trans- I missions. Tin-hare racing in Australia must be : most exciting if one can judge from j the excitement of the announcer in ■■ Sydney' while describing the event. SHORT-WAVE RECEIVER Owing to the interest that has been taken in the short-wave set designed by Mr. Russell, of Christchurch, and mentioned last week, a diagram of the circuit is being published together with a list of the components used, j •‘The Sun” short wave receiver is not j I a complicated machine, and the ordin- I ary short wave receiver can lie con- j verted to this model with very little j trouble. A glance at the diagram will show that the grid leak and condenser have been done away with and that the plate rectification method is employed. A volt G battery is used, the positive of the battery going to the moving arm of a potentiometer, which sliould be about 400 ohms in value, a

fixed condenser of at least .005MF byepasses the C battery and potentiometer to the negative filament. Note that all rheostats are in the positive lead, and that the positive of the C batteries and the negative of the B battery is connected to the negative filament, which is also connected to ground. MATERIAL REQUIRED. 1 Set of short wave coils, Aero, Bremer Tully, Radio Supply, etc. 1 .000125 MF variable condenser of GOOD MAKE. 1 .00025MF variable condenser of good make. 2 First-class vernier dials, having no backlash. 2 UX cushion valve sockets. 1 Rradlevstat. 1 30 rheostat. 1 Bradleyolim 25.000 to 1,000,000 Ohms. 1 IMF condenser. 1 .005 or larger fixed condenser, 1 400 ohm potentiometer, Centrclab, or DeJur. 1 Choke coil. 1 Filament switch. 1 Single circuit jack. 1 5-1 Audio frequency transformer. 2 UXI99 valves Condor or RCA. 1 4£ volt C battery. 1 H volt flashlamp battery. 1 7 x 14in panel. 1 Baseboard. Ebonite strips, terminals, busbar, screws, etc.

PRICE REDUCTIONS Current literature from England indicates substantial price-reductions, especially in the prices of valves and B battery accumulators. Some of the j valve reductions are as much as 7s Gd j a valve, but whether that will be ef- | fective here remains to be seen. One may see a small reduction, but even | that, to the writer’s mind, is not very j likely, as even with the new prices the same valves are still more expen- , sive in England than they are here, i The price of B accumulators has dropped in some cases of very high-class makes to 7£d a volt, and a convenient carrying crate is now supplied free with the units. FURTHER NOTES ON A.C. VALVES j To compete successfully with batj tery-operated receivers, it is essential I that sets employing A.C. filament I valves compare favourably with them in respect to all important operating j characteristics, including tone quality, volume, sensitivity. selectivity and freedom from hum, power-line disturbances and services troubles. The cost and weight of component parts are also an important consideration. One of the most important requisites for obtaining true tone-quality is the use of a valve in the last stage of the audio frequency amplifier, that is designed to handle the necessary power output without distortion. Used in this j stage, the suitable power or super- | power valve may have ixs filament heated by raw A.C. of suitable voltI age, provided that there is a suitable resistance, with a centre-tap for the grid return, and the proper plate and bias voltages. Given these requirements the operation will be as satisfactory as if the filament were heated by a storage battery. To obtain freedom from line disturbances, care must be taken to pre-

vent the direct pick-up of such disturbances by the valves and associated equipment. Power transformers should be shielded if placed in the same cabinet, and sometimes electrostatic shieldings between the primary and secondary windings of the transformers are necessary. The rugged design of A.C. valves insures freedom from service troubles as far as the valves themselves are concerned. By the elimination of all devices requiring corrosive liquids, the possibility of corroded connections disappear, and it is evident that, with proper care in current design and the use of highgrade parts a greater measure of freedom from service troubles can be secured than has been possible with previous designs of radio receivers. Furthermore, the annoyance of stor-age-battery attention, or the trouble and expense of dry-cell renewals, is removed by the use of a receiver which draws all of its electrical energy from a convenient house lighting socket. With respect to the cost and bulk of the component parts, this A.C. valve combination is particularly satisfactory since the use of a heavy and expensive A-filter system or A-supply unit is avoided, for the necessary A voltages may be obtained by adding a few turns of wire to the power transformer supplying the plate-voltage unit, or by the use of a small separate transformer designed for this purpose.

CATERING FOR THE U.S. FARMER The Department of Agriculture in the L T nited States has brought forward an extensive service for the American j farmer, and this is the result of special study on the department’s behalf, j The programme includes housekeeping information, such as marketing, cook- | ing, gardening, etc. A radio farm 1 school gives practical information on poultry, dairying, livestock, crops and I soils, farm economics and much other • useful information. A special feature is the manner of offering this informa- ! tion. Much is done in the form of a dialogue between two people, one ask- j ing questions and the other giving the information in reply to the questions, and in this way the interest is sustained.

MODERN ADVANCES At the Radio World’s Fair in New York many marvels of science are to be displayed. The smallest voice in the world, that of the atom, will be magnified 20,000,000 times so that the human ear may hear it. By means of this new device the language of flowers, the voices of hitherto silent insects can be clearly heard. The ma- i chine is so sensitive that the growing 1 of a rose sounds like thunder. Methods of measuring accurately lengths of one ten-millionth part of an inch will be shown and described. Furnaces will be shown using high-frequency currents which will melt metals, at the same time feeling quite cool when the hand is placed inside. On the other hand this same energy will be used to produce extreme cold, causing mercury to become as hard as iron and flowers as brittle as glass. BROADCASTING ON THE BEAM With the beam service established for telegraphy between England and Australia, the directors of 3LO, Melbourne, with their characteristic enterprise, have applied to Amalgamated Wireless for permission to use the beam service for the purpose of transmitting an Australian programme to England for rebroadcasting there. With the success already achieved by P.C.J.J., the use of the beam should give results very much better than any so far achieved. The signal intensity received in England should be many times greater than that got by any other means and this would have the big advantage that transmission would be possible at any hour to suit the British requirements. In addition, fading and interference from static would be much reduced by the use of the beam system. The present system, although not meant originally for telephony, could be made to transmit a musical programme, with alterations to the equipment estimated to cost between £2OO and £4OO. It is understood that 3LO is prepared to spend several hundred pounds in making the experiment, but so far no reply has been received from Amalgamated Wireless. If this experiment proves a success, it will be an adequate answer to the critics who consider that the British Broadcasting Corporation should have embarked on a shortwave station to serve the whole Empire, at any rate as far as Australia is concerned.

PROGRAMME EXCHANGES Some time ago, an experiment in the ■ exchange of wireless programmes was carried out between 3LO and 2FC. By arrangement with 2FC, 3LO was able - to broadcast “Madame Pompadour” ‘ from Sydney at the same time as it * was broadcast by 2FC. Later, in re- ( turn, 2FC broadcast a description of a 4 wrestling match at the Melbourne g Stadium at the same time as 3LO. This exchange of programmes is being 1 extended. A few days ago, by ar- £ rangement with 3AR, the Hobart station 7ZL broadcast the whole of one of c the programmes from 3AR. In this f case, the programme was picked up in i Tasmania by wireless, instead of being t

I transmitted by land line, as was the j case with the exchanges between 3LO | and 2FC. It is now announced by SCL | that it proposes to devote portion of next Thursday night to the transmission of part of the programmes from : one after another of the other Australian stations. The interstate stations will be tuned in on a sensitive j receiver, and the transmissions will be relayed by land line to SCL. It is satisfactory to see this increase in interest in the exchange of programmes i between Australian stations. A great j measure of the success of the British I broadcasting system has been due to j the excellent facilities which have been , provided for the exchange of pro-

grammes between the stations. This means that if one station has an item in its programme of more than ordinary interest, it can be broadcast in other States for listeners there. The wisdom of using the transmission from the interstate station as the medium of rebroadcasting, however, is open to doubt. If an interstate transmission is : picked up and rebroadcast, all the \ original faults due to atmospherics and j fading are also rebroadcast. The use jof land lines for relaying gives far 1 better results.