ON ALL WAVELENGTHS

Evening Star, Issue 20440, 22 March 1930, Page 8

ON ALL WAVELENGTHS

By

RADIO FOR AIRCRAFT. i Testimony has recently been borne to * the value of radio as a means of guiding aircraft. The utility of wireless in J this connection is well recognised in , 1 England, Europe, and the United States | ' of America, and the case of the British | f airship RIOO remaining over the | < English Channel all night without j k being in sight of land has directed at- I ' tention to the relation between various I * forms of wireless communication 1 and air 1 • travel. The commander of the RIOO I*■ reported that he knew exactly where he j * was at all times, having constantly • taken cross-bearings by wireless. Thus } it was a simple matter to calculate his 1 position. There is a strong body of £ opinion in Australian radio circles that tne airways of Australia should be made 1 safer by means of radio .On at least 1 three occasions during the historic < flights of the Southern Cross radio j beacons would have been of great value J to'the navigator of the machine in 1 enabling him to learn the exact posi- f tion of the aeroplane during storms. < There are three principal methods by 1 which aircraft in flight can be assisted by radio, all of which might be used i 5 with advantage to develop national air ] services. These methods are— j ■- (1) The use of a transmitter and \ receiving set on a plane, by means of j which an airman can signal to ground 1 stations. The latter, being fitted with j direction-finding apparatus, can in a J few minutes plot tne precise position 1 and acquaint the aviators. < } (2) A station can send out two < signals at an angle of about 90deg. These are received by the pilot. Pro- ] vided that they blend at equal strength i he knows that he is travelling straight 1 for the signal; otherwise be must veer < either to the right or the left accord- ■ ihg as the signals come in strong or 1 weak. 1 i(3 A plane can carry direction-find 1 ing apparatus, by means of which it can -i fly straight to a given station, either a * broadcasting- station or a wireless bea- '• bon. ' ■' < „ ■ - i i. i : . < > ..... i iTIPS FOR -A.C. SET BUILDERS. , Several vital ' points have- to be watched in" the' construction of any ■ . completely A.C. operated receiver A’ 1 Correctly constructed and adjusted A.C- j set will, have, practically iiq hum. in j its output, and will only be distinguish- ( able in its" opera tion from a battery set i ' when head phones are used. _ j ’ Presuming , that the “B ” eliminator I 1 is giving a good pure output, hum can I ! her brought into an A.C. receiver! 1 through faulty construction. Grid ! leads, especially if running (dose and 1 parallel to an A.C. carrying lead, will 1 produce a 60 cycle or a multiple of 60 cycles hum. If the detector grid ’lead is at fault, the hum will be amplified in the audio stages, and will repro-. duce itself in thb form of a loud and 1 annoying rattle, which will all but i 1 drown the music. 1 In the A.C. receiver all the •Id : 1 “haywire” methods must be dispensed I | with. . Many, set-builders like do de- 1 1 sign their own layouts, but,, if they ! have had no previous experience with j A.C. 'set construction, it would be 1 wise for them to save disappointment by following the lead of one who has. The valve sockets, coils, and audio ■ coupling apparatus should he placed with an object. This object is to keep oil A.C. filament and beater leans together iiv-the form of a twisted cable running right along the back of •‘he baseboard. All the grid and plate ter mmals of the valve sockets and audio transformers, chokes, or resistances should face the panel of the set thus allowing all the connections being made to these terminals without coming no»r any A.C. carrying leads. Do not attempt to wire in’ the A.C. filament and heater circuits as . you would in a battery set. Each pair of A.C. carrying leads must be tightly | twisted so that the field surrounding each lead is confined within a distance of a fraction of an : nch around ; the flex. In any A.C. receiver the importance of short grid leads cannot be over stressed. Trouble will often arise when a pick-up switch is wired so that this instrument is connected to the grid of the detector v nlye. A pick-up switch, connected in this manlier, must be located as close as possible to the detector valve, -bus having a short grid, connection to the switch. A long lead here will result in cis tortion and a had hum. , To illustrate the importance of perfect wiring and insulation in an A.C. set, drive the screw into the wooden baseboard of any A.C. set, and connect it to the grid terminal of the detector valve socket. You are now getting the same effect as you would if the grid leak clips were screwed to the baseboard or the grid lead wore touching the board, i Trouble of this type may for weeksbaffle the novice, hut he has only himself to blame as no connections should touch the baseboard, which, Oven if thoroughly dry, will sooner or later have a thin layer of dust over its surface, ' Correct placing of the heater transformer of our A.C. set calls for some I thought.. If it is to be located near the tuning coils,,. hum will be sure to; originate in the detector grid cir-j cuit. The best plan will be to place | it'at the speaker end-of the set, as far away as possible.from: - any of the amplifier coupling devices, whether theybe transformers, chokes, or re-The-heater transformer should be shielded with iron or steel, as this is the only' material which will confine the field surrounding this component. The shield must also be, earthed. So much for hum in the actual receiver. •Incorrect centre tapping of a boater transformer will result in a , certain amount of hum in the final l output. Our aim is to do away with all hum and this can be done. Should a filament or heater transformer secondary not give an absolutely equal voltage reading each side of the centre tap, a resistance must be used to obtain the centre tap connection. A 200-ohm potentiometer will take a current of 30 mills when placed across- a 6-volt secondary. This current is negligible. . By connecting the centre tap connection to the moveable arm of the potentiometer, hum in this quarter can be entirely obviated as an absolutely accurate adjustment can bo obtained'by the simple process of turning the potentiometer knob and listen-

NOTES AND COMMENTS /

ing for the absence of hum in the final output when using headphones. So far wo have discussed likely sources of hum in the circuit and heater supply. ,If a battery set is used with an eliminator to give a humless output, the eliminator need not he considered as a source of the hum. Still, there are faulty eliminators, and we can discuss what can be done to eliminate hum from this source. If the faulty eliminator is of a commercially built type which normally gives a clean output, the best plan will be to change the job, unless, of course, it ban broken down after having been in use for some time, and no guarantee was given; with tho unit. Faulty centre-tapping of a high voltage secondary in an eliminator, when using full wave rectification, does not result in as great a hum in the output as would be expected. ’ I have used in an eliminator, a transformer which gave 320 volts on one side of the centre tup and 260 on the other, yet a pure output ‘ was obtainable. ’

Centre tapping of the high voltagesecondary by means of the. resistance method is obviously * impracticable, and if the transformer possesses this defeet, the trouble must be remedied byi improving the filter circuit. This can be don.e, and, considering the work required in the balancing up of two high voltage secondaries after a transformer has been finished and varnished; or waxed, it is well worth the expense j of the extra filter condensers. i

Inadequate by-passing of resistance. 1 voltage dividing tappings will result in hum. The usual capacity is .01 mfd., but on the detector and first amplifier tappings, this capacity should be increased to two or four microfarads; When thermionic full-wave rectification is used, the centre tapping of the rectifier filament heater .secondary does not call for the same accuracy as in tho receiver. However, | a serious discrepancy- in the voltage , on either side of the centre tap might | call for the substitution of the poten- ■ tiometer method as, tho best means of obtaining the centre oi tho filament heater secondary voltage. . 1 Inadequate filtering after any rectifier will result in hum, and it is not a wise practice to try to save a few shillings by omitting a filter condenser here and there. The home-made eliminator should be shielded, not with copper, but with steel or iron, as this material will confine the field surrounding the transformers and chokes used in its construction. This shield should also be earthed. Correct shielding will permit of the eliminator being used close to tho receiver with no trace of hum. I There is no doubt that tho output from the thermionic full and halfwave rectifier is easier to .liter than any of the gaseous types, but this should not prevent use of the latter; typo. I have, for the past four years, used a gaseous ' full-wave; typo rectifier which was one of the,- first to land here, when eliminators were practically in their infancy. This tube has been subjected to heavy overloads, but is still delivering a humless output with plenty of current, quite enough for any five-valve r.f. receiver using a power tube in its amplifier stage.— “ Listener Id.” _ INTELLIGENT LISTENING. In the 8.8. C. Year Book, for 1930 there is a chapter on ‘ Intelligent Listening.’ The chapter states, inter alia, that one of the reasons why broadcasting is not universally cultivated by people who are most able to avail themselves of its services is that wo do not sufficiently use discrimination in our listening. We have attempted times out ot number to explain to listeners that broadcasting has to coyer . so., many phases in which aot an individual, but a million listeners, have to be reached iu a day’s broadcasting activities. It stands to reason that a broadcasting programme* will not always measure up to expectations. When we are wanting a classic programme and are . being treated to a song scena instead, it does not do to immediately castigate tho broadcasting programmes because our particular taste is not being catered for on that occasion. Our turn will come another time. A good plan is to treat our broadcasting programme as we do our theatrical entertainment. Before we go to a theatre we do not as a rule choose a talkie or a play haphazardly without first having ascertained something about either,, so with our broadcasting. Before we listen in to an evening’s entertainment it would behove us to scan the daily programme and find out what is on for our entertainment. After having selected the items we want, tune into them at the times prescribed, and tune out of them when they are finished. That is the secret of the success of intelligent listening. To hear what we like gives us a pleasurable feeling, and broadcasting should give listeners that if we will only learn how to use our sets with discrimination by not abusing our ownership of them by having the wireless turned on from early morning till late at night. According to the 8.8. C., ■> very much more selective use would be made of. programmes if we looked at the programmes beforehand and decided what we wanted to hear. Tho 8.8. C. states: “ It is the common failure to exercise intelligently this privilege 1 of selection that has kept so many intelligent people from giving broadcasting a regular and appointed place in their hours of leisure.” To be an intelligent-listener capable of constructive and not destructive criticism is not hard. It requires only the exercise of a little thought in our likes and dislikes in broadcasting programmes. Listen in to what we want to hear—tune out what we do not want to hear. Broadcasting is, after all, a privilege ■vhich, like most privileges, should not be abused. If we curtail the use of our wireless s-’t to so many hours a week it will be within the reach of all to o solution to a delightful and valuable entertainment.

STENODE RADIOS!AT. AN ALL-BRITISH INVENTION. Known as the stenode radioptat system of radio communication, an all- . British invention was recently tested by a ‘ Daily Mail ’ reporter. The invention, it is claimed, assures traffic control in the ether. The inventor. Dr James Robinson, formerly chief of wireless research for the Royal Air Force, stood beside tho mystery box. Before tho test was made it was claimed that as a result of.the invention— Many more European broadcasting stations will be able to find “ channels” on the ether. At present, with the channels 9.000 cycles wide to prevent one station from interfering with another, only 110 channels are available. Howls from neighbours and interferi ences of all kinds will become a thing of the past. Listeners will be able to go silently and' efficienty from one European programme to another. . Ten thousand words a minute can be telegraphed. The telegraphing of unlimited pictures will be facilitated. The cost of telegraphy and telephonywill be greatly reduced. Ten times the amount of traffic can be carried over existing telegraph and telephone lines. For tho purposes of the test, a room near Oxford street west was fitted with an ordinary valve receiving set to which the mystery box had been fitted, an ordinary valve receiving set without this attachment, and a set which transmitted shrieks and howls and sundry other noises across the room on a frequency only fifty cycles removed from that of 2LO. Fifty cycles are 1/180th of the width of the channel permitted between broadcasting stations. Both the valve sets were tuned in to 2LO (and therefore to the noisy transmitter across the room), and reception was begun On tho valve set which was not fitted with the mystery box the music of 2LO and the din from the transrrtter in the room came through in an indescribable medlev of noise. No amount of tuning would separate the din and tho music. On the set fitted with the mystery box it was possible to tune out 2LO or the noisy transmitter at will. Tho inventor of the mystery box said: “We are not going to 'sell -b----box. Manufacturers will be invited to incorporate my invention in the sets they build. “In my opinion, it will not add tthe cost of a.good set. It will, in fact, cheapen the cost .in certain circumstances. In'America a six or sevenvalve set is often necessary because of tho great number of stations on tho air—the owner paying more for his set to secure adequate ‘ filtration,’ so to speak.” Dr Robinson said that between the wave-lengths of 300 and 600 metres they could in future, employ 5,000 stations. whereas at present the number was only twenty-five. Without absorbing much space in the other it would be possible to transmit at the rate of 10.000 words a minute. It would bo feasible to telegraph the whole contents of a daily newspaper in a few minutes, both reading matter and pictures. Instead of paying so much a word the rate in future would be so mu oh per inch. The device could also be applied to existing land telegraph and telephone lines, enabling them to carry ton times the. existing amount of traffic. Colonel Simpson predicted that the time would come when Empire newspapers would be published simultaneously in London, Cape Town, Sydney, Montreal, and Calcutta.

TELEVISIOb STATION AT WASHINGTON. A high-powered television broadcasting station, owned by Mr 0. F. Jenkins, the well-known television expert in America, and located at Washington, has been established. It broadcasts visual images on a wave-length of 103.4 metres with 5,000 watts. The aerial system is supported between two lattice steel masts each 128 ft high, spaced 200 ft apart, and is of the cage typo, with a counterpoise earth system. The station is actually functioning at the present time with a daily schedule, transmissions being given between the hours of 8 p.m. and 9 p.m., and sends out moving pictures by means of the Jenkins system. The whole station and studio are housed in a building of the bungalow type. In the studio there is a motion picture projector with its film reels, together with the usual television scanning discs, photo-eloetrio cell equipment, and radio amplifier. The last is employed for the purpose of magnifying up the feeble electric impulses produced by the photo-electric cell from the light variations falling on it from the moving film. In the adjoining room is located the actual radio transmitter, which is capable of dissipating 5,000 watts. Its design is slightly different from the ordinary broadcast transmitter in that special care has been taken meet the particular requirements desired for the faithful transmission of images on carrier waves as compared with those necessary for sound transmission. A 5-kilowatt water-cooled valve is employed for generating the wireless waves, and it is anticipated that with this valve signals will bo received over the whole of the eastern half of the United States.

The first broadcast establishing this new service was the transmission of a silhouette showing n small girl bouncing a ball. Apparently this scene depicted a romantic side of Jenkins’s work in that this was one of his first efforts in connection with the television art. This was followed by a long film entitled ‘ Call It Love.’ , A further studio is being erected at the station, whence it is hoped that by means of his latest apparatus likeness of living objects will be able to be broadcast, which is television as wo know it in this country.

Question at county court: “What did your husband say when ho discovered the broken receiving set?” Wife: “May I write it down?”

CHARGING THE ACCUMULATOR. MAINS NOT REQUIRED. For tho accumulator charger to be described no power, supply is needed This charger is described more especially for country listeners where houses are not connected with the mains. The material required for the building of the charger is as follows: 0ne.218 glass jar fitted with a wood stopper about Jin thick, with a centre hole to take 2 B.A. screwed rod, and another hole near each edge, one to thread a wire through and the othei to allow any gases to escape. About 2Jin of 2 B.A. screwed rod, with two nuts and a terminal head. A block of cast zinc about fin or fin thick, round or square, as largo as will comfortably go into tho neck of the jar. A strip of copper about 6in by IJin and about l-16in thick. A piece of fairly stout insulated copper wire. One pound of sulphate of copper. Tho zinc can be cast at homo quite easily. Obtain some old zinc or any zinc scraps, and melt them down in an iron ladle or similar receptacle. When thoroughly molten pour out carefully into a rusty tin lid the required size. Use a rusty lid, as tho block will easily drop out of it. When the zinc has been poured the end of the screwed rod, held with a pair of pliers, should be pushed into the centre of the molten metal, and held there until the zinc has set. When cold polish the bottom surface of the block with sandpaper or an old file. The 2 B.A. rod may then be put through tho wooden cover, with one nut above and one below, and both tightened up. Then nrep.aro the copper strip, and the insulated wire must be riveted to this with a copper rivet. No solder must bo used anywhere in the battery.

A FEW TIPS. The following tips to simplify matters in connection with radio have been sent in by “ Duplex ”: To tin a soldering iron permanently take it to a jeweller and have him tin , the point with silver solder. This has j a higher melting point than lead solder, I and the point will stay tinned. It is best to let a jeweller do the work, unless you are accustomed to using hard solder. The cost is very small. I ♦ * * * | Threading a nut behind a panel or under the receiver is made easy if a length of- busbar wire is bent to hold the nut. This means that the wire will be able to reach in places where the fingers cannot. # a # Wireless Proverbs.—New sots get new stations. Mendings aro honourable. An old man with a headphone is a good sign. The higher the plum tree the better the plum; the higher the aerial the better the tune. “ Duplex ” also supplies a few jokes that should make pleasant light reading for the wireless man. , They are published elsewhere in these columns. Further tips that would benefit the wireless listener would be welcomed. STRAY SPARKS. The linking of six stations in New Zealand on Tuesday afternoon for the purpose of letting all school children near Rear-admiral Byrd’s address at the Town Hall worked very well. Private reports from Invercargill indicate that 1/jp in that city put tho address over quite well, while 2YA Wellington, 2YB New Plymouth, IYA Auckland, and 3YA Christchurch were also good. For those children in Dunedin who were not taken to tho Town Hall 4YA broadcast the address and wireless sets wore installed in many of tho schools. » « * # There was a big radio bonfire in Philadelphia recently, when 1,000 obsolete receivers were burnt in order to relievo the market from these out-of-date sets. Tho dealers made generous allowances on each set, provided a new «et was purchased. • • • « in order to distribute news more rapidly American newspapers are to employ special short-wave transmitters for 1 use between the Pacific and Atlantic coasts. With Chicago as the central point transmitters are to be built at Now York, Boston, San Francisco, Los Angeles, and New Orleans. « • • • When it was known in America that Sir Harry Lauder was to broadcast listeners all over the country sent in requests for their favourite Scottish airs, and it took over a week for a staff to sort tho letters and tabulate the requests. WIRELESS WIT. Auntie: “Tommy tuned in like a man. Mother; “I didn’t think he’d make all that fuss.” ; • • « # John; “What’s become of young Jones and his money?” Jim: “The young fool’s been playing knobs and valves with it.” John: “How?” Jim: “ Ho put it all into a wireless firm,” Husbancf and wife wore visiting friends, and were waiting in the drawing room. In front of them a picture of a loud speaker was hanging on tho wall “I wonder why they hang that picture,” said the wife. “ Perhaps the artist is broadcasting to-night,” answered the husband. • * * • Five-valve portable wiroloss( owner going abroad) for sale. Cause and effect. CORRESPONDENCE. “ Voltage ” (Mornington) writes: * I have built a battery charger using a Philipps 1,010 full-wave rectifier, itdelivers 30 volts at 1.3 amps. Would this voltage be harmful to a 4 or 6volt A battery? 1 intend to use this voltage to charge 20-volt hlpcks of wet B batteries (four_2o-volt blocks in parallel). What resistance would I require to break the amperage down to 100 milhamps for the B battery?” —The charger would be suitable for charging the B batteries as you state, and the correct milhamps charge could bo found by experimenting will) a 70watt house lamp in series. For charging a 4 or 6-volt A battery the writer would suggest that the charger be altered to 8 to 12 volts maximum output from the tube.

The diagram shows the assembly of the coll. l'he copper is lowered into the jar, and lib oi copper sulphate (crystals or powder, but preferably crystals) poured in and levelled off. The end of tho wire is then threaded through tho cover. Before closing up tho jar tho underside ot the lid and the top of the zinc should be thickly smeared with vaseline, and it would be well to smear the whole length of tho wire as well. All is now ready for closing up. Fill with distilled or boiled water, poured in slowly, up to about J-in below the wooden cover, and then push the cover firmly into its place. The whole of the cover should now be covered with molten wax, which will seal the joint between the wood and jar and prevent creeping. Before pouring the wax place a piece of wood or a match stick in tho vent hole; this may bo withdrawn after tho wax has set. Great care should now be taken not to shake the jar, which should be placed where it is intended to rest.

Eight of these cells connected tn series will keep a 4-volt accumulator fully charged w'hen used and connected through a double-polo, double-throw switch, as illustrated. When the battery is complete and all the coils connected in series fasten two pieces of copper wire or two pieces of zinc to tho remaining positive and negative poles, and immerse these in an insulating jar of clear water; keep the ends as far apart as possible in tho water. Tho whole should be left in this position for four or five days, when it may be connected up to tho switch for use. Tho wire is the positive and the terminal the negative pole, and must be connected to the accumulator in parallel, positive to positive and-negative to negative.