WIRELESS NEWS

Press, Volume LXVIII, Issue 20612, 30 July 1932, Page 6

WIRELESS NEWS

(By "Max.") I have received a copy of the report of the Broadcast Coverage Commission. As there are some 50 pages, it is impossible to reproduce it in full, but after the matter has been studied summaries of interesting features will be given. A brief survey of the items of most importance has already appeared in other columns of The Press. The report deals with the following subjects in the order indicated. (1) Outline of tour of investigation. (2) Belevant points arising out of tour: —(a) Heterodyne interference of New Zealand stations; (b) Power interference; (c) Location of transmitting stations; (d) Incidental advantages arising from widely separated regional stations; (e) The part played by the receiver; (f) The effect of wavelength on propagation; (g) Community of interest. (3) General comments on points raised in order of reference; (a) Distribution of population; (b) Topographical features; (c) Practicability. of having one or more national stations giving non-fading reception all over the Dominion; (d) Desirability of establishing relay stations, and means of connecting same with distributing centres; (e) Power of stations; (f) Adequacy of existing stations; (g) Modern features Of design with respect to new and existing stations; (h) Ultra short-wave broadcasting. * * Not only home experimenters but also all prospective set-owners and those who desire to make a change to a new receiver will be pleased to know that a new type of valve has been developed by Standard Telephones and Cables. It is called the "Micromesh," and extremely close spacings are utilised between the emitter and the control element. Up to the present timo two difficulties have prevented this method from being used. The first is mechanical rigidity and the second the fact that if the grid is too closo to the cathode, the former becomes hot enough to cause it to have matter deposited upon it from the adjacent cathode. It then gives off electrons itself and distortion occurs.

Mechanical rigidity is secured in spite of quantity production requirements, by constructing the valve as a unit. All tlie elements aro fastened to upper and lower mica insulators, which aro accurately punched in a press. The electrodes aro secured to these mica bridges at the top and bottom, the whole forming a unit quite independent of the stem, so far as accuracy is concerned. It is therefore possible to close space the emitter and the control grid so that much better characteristics are obtained. The heat which would otherwise cause the grid itself to emiU electrons is radiated away by a fin of special design, and this is so efficient that even with the cathode and anode at red heat, there is no emission from the grid. The cathode is free to slide at one end in the direction of its length, and so cannot warp and make contact with the heater or grid. This touching of heater and emitter occasionally occurs in valves, and means a replacement.

Three types of "Micromesli" valves are being constructed already, and one is a detector with an amplification factor of SO, a mutual conductance of 8 milliamps per grid volt, and an A.C. resistance of 10,000 ohms. This is a remarkably high mu for a three-elec-trode valve, but the type P.A.I has a mu of 12 mils per grid volt, with an impedance of 1050 ohms, and the high amplification factor for a power valve of 12.C. In the course of a few months a screen grid typo will be evolved and if the characteristics make a proportionately good showing, then set manufacturers should give us greatly improved receivers.

A Jcvrell valve tester recently was demonstrated to the writer to show the capabilities as well as tho working. The unit is extremely simple in appearance and there are not many switches to make it difficult to master the operating. Being A.C. fifty cycle design no batteries are required. A very long needle moves over a colour schemed scale. To test a valve, it is inserted in the correct socket, of which there are several •to cover the various types, two meters are noted, and two adjustments made to bring the dials to zero. The big needle deflects, and the reading is taken, all that is necessary being to run along the list ot valves marked in a row. If the needle swings well into the centre of the correct colour, the valve is good for anodo current taking requirements. Simple tests show whether shorts are present/ between any pair of elements. A 558" rectifier which was tested showed that the plates gave similar currents within an extremely small margin. .This feature alone is valuable, for the ease and rapidity with which the tests can be made appeals to the keen radio enthusiast. In the colour scheme," eactt type of valve has its own horizontal column, and the colour bands (there are two, from memory) are proportioned to suit the valve characteristics. Green and pink are the two colours, one denoting a valve below standard, and the other a normal one. A red light shows up immediately the machine is in operation, so there is no excuse for forgetting to switch off after using the tester. When trying tor shorts between elements, two separate coloured lights are used, one for eacJi type of short.

It appears that the first report that the outpost station, during the recent IL'E.C. field day, failed to contact with the zone station was incorrect. Signals from the outpost were received by distant stations at good strength, and the wave-length specially assigned for emergency working or testing only is considered to bo most suitable. Carelessness when disassembling resulted in three valves in the receiver burning out.

Wireless Weekly, Australia, gives a design for a powerful amplifier suitable for a gramophone using a class "B" system. In all, four valves are required. First a 227, which is transformer fed to another of the same family, and this is coupled to a pushpull stage of a pair of type '46's. Tao class "B" method utilises a bias ou the outpiit stage whereby the plate current drawn by the two tubes is almost zero with no input. When a strong signal is impressed upon the grids, the grids go positive alternately as the voltage rises to the maximum at each half cyclo. The other grid will be simply more negative and well, below cut-off current point. A larger input voltage than is used for the ordinary amplifier is required, naturally, to cause the grid to sweep over to the positive side, but there is no noticeable distortion. When in operation with the -maximum permissible input, the output valves draw quite a large current and thus give a big output.

In the Australian Commonwealth there has been a prohibition against the importation of radio receivers and parts. The Minister for Customs states that this action has been justified because of the condition: of the radio

Notes From Far and Near

BROADCASTING. TODAY'S PROGRAMMES. SYA CHRIBTGHTTK.CH <9BO Kilocycles.) 3 p.m.: Gramophone recital. 4.30: Sports results. 5.0: Children, by Aunt Pat and Uncle Charlie. 6.0: Dinner music. 7.0: News and reports. 7.45: Talk, Mr A. H. Bridge, . "Town Planning" (No. S), "Zoning." 8.0: Concert programme. Relay of programme from 4YA, Dunedin. 3 0.0: Wports summary. 10.10: Dance music. 3ZC. (1200 Kilo.) 6.30-6.15 p.m.: Children's session. 6.156.45: Dinner music. 6.45-7.15: Sporting and general news. 7.15: Musical items. 7.45: Contract Bridge Talk (Mr W. Shackle). 8-10: Concert session. 10-11: Dance programme. 2YA, WELLINGTON (720 Kilocycles.) 2.45: Relay. Description of Rugby Football Match, played at' Athletic Pork. 5.0: Children, by Aunt Molly and Uncle Jasper. 6.0: Tinner music. 7.0: News and reports. 7.30 W.E.A. Session: Professor T. A. Hunter, "Man and His Social Institutions —Social Institutions in the Machine Age." 8.0: Concert programme. Relay from the Concert Chamber, Town Hall. Concert by Wellington Commercial Travellers' aud Warehousemen's Association Mai© Voice Choir. 9.0: Talk, Mark Nicholls, "Some of My Contemporaries." 10.0: Sporting summary. 10.10: Relay of Dance Music from the Adelphi Cabaret. SUNDAY. 3YA, CHBISTCHTTRCH. 2 Gramophone recital. 5.30: Children's Song Service by Children of Congregational Sunday School. 6.15: Musical rhimes. 6.30: Relay of Evening Service from Trinity Congregational Church. Preacher, Rov. D. Gardner Miller. Organist, Len Boot. Chair Conductor, Jas. Shaw. 8.0: Concert programme. Selected recordings. 8.15: Christchurch S'alon Orchestra (Conductor, Francis E. Bate), "Tho Three Bears" Fantasy (Coates). 8.25: Choral, Edge ware 'Road Methodist Church Choir, "Hymn to Music" (Buck); Anthem, "At Even Ere the Sun was Set" (Hancock). 8.32: Recording (Organ), Sandy Macpherson, "Tho Monk's Dream" (Holmes). 8.35: Mrs 11. Queree, "In the Woods" (Frani). Bass, E. J. Johnson, "The Dover Patrol" (Carrington). 8.40: Part' song, The Choir, "As Torrents in Summer" (Elgar). 8.42: Sulon Orchestra, "The Merchant of Venice": (a) "Prelude"; (b) "Portia"; (c) "Inge's March" (Rosse). 8.51: Contralto, Hilda Smith, "The End of the Lane" (Kennedy) Russell). 8.55: Choral, Road Choir, "O Father, Whose Almighty Power" (Handel); "Gloria" (Twelfth Mass) (Mozart). 9.1: Weather forecast and notices. 9.3: Recording (Piano), Karol fi/.reter, "Liebostrauroe No. 3" (Liszt). 9.7: Baritone, E. B. Ohambers, "Little Boy Blue" (Nevin). 9.10: Recording (Monologue), Will Kings. "Not Understood' (Bracken). 9.12: Choral, Edge-ware Road Choir, "Sweet is the Sunlight" (Eggleston). 9.17: Salon Orchestra, Three Dances from "Tom Jones": (a) "Morris Dance"; (b) "Gavotte"; (c) "Jig" (German). 0.25: Recording (Tenor), RJcbard Tauber, 1 Loved Yon More" (Jurmann). 9.28: Recording (Violin), Frederick Fradkin, "Frasquita" (Lehar). 9.31: Metso-soprano, Anne Lucas, "The Pipes of Pan are Calling (Monckton). 9.35: Recording (Harp), Mildred Didding, "At tho Spring" (Zabel). 9.39: Soprano, Jessie Duff, "Sunshine and Shadow" (Hampton): "The Birth of Morn (Leoni). 9.43: Recording (Tenor), Francis 'Russell, "Eric's Song" (Wagner). Recording (Organ), Reginald Foort, In the Heart of tho Sunset" (Nicholls). > 9.50. Edgeware Road Choir, "The Day is J*®"* and Over" (Marks): "When Evening Twill s-ht" (Hatton). 9.55: Walts. Salon Orchestra, "Tales from, the Orient (Strauss).

3ZC. (1200 Kilo.) 10-11.00 a.m.: Selected items. G. 15-8 p.m.: Dinner music And selected itoms. 8-9.50: Concert session. ' 2TA, WELLINGTON. 2 p.m.: Selected recordings. 6.0: Children's Song Service, conducted by Uncle George, assisted by tho Children's Choir from St. James's Presbyterian Church. 7.0: JJelny of Evening Service from St. Gerard's Kedomptorist Church, Hawker Street, Wellington. Preacher, Itov. Father Croagh. Choirmaster and organist, Messrs F. J. Oakes and 11. Mount, respectively. 8.15 (appro*.): Concert programme. Relay. Concert by the Port Nicholson Silver Band (Conductor, J. J. Drew).

business in America. In that country there has been over-production, considering the depression, and many manufacturers have been prepared to sell sets at prices' considerably below normal. Apparently this would have seriously prejudiced the Australian manufacturers' prospects, and the home industry could not be allowed to be swamped by foreign productions at prices against which locally-built receivers ■ could not compote. ■» •* It will probably puzzle some people to know how it is possible to build up oscillatory circuits suitable for those extremely ultra high frequencies corresponding to wavelengths below one inch. It would seem impossible to make condensers and coils to tune so low. A five metre outfit usees a few turns of wire a little over one'half inch in circumference, but to design for waves which are one-fiftieth of this appears a problem. It was only upon the discovery that the elements of the valve itself could be made to perform the necessary functions that these microscopical waves were possible. Tf the grid is made highly positive and the plate slightly so, or perhaps negative, then the high potential upon the former will draw electrons from the filament at a great velocity. A number will actually strike the grid, but the majority will speed right through, but the moment they start to travel away from the grid, the latter is drawing them back again, but the ; y go a short distance before their velocity is reduced to zero and the return journey commences. By the time they arrive at the grid again, they have acquired a big speed again, and once more the greater number passes right through. This process is repeated and the rate can be accelerated by a negative potential upon the plate. ■ The latter acts bv repulsing the electrons which shoot through the grid on the outward travel and thus shortens tho time necessary to bring them to a stop prior to a return towards the grid The potential on the grid is sometimes as much as 250 volts and the swinging backwards and forwards of the electrons constitutes a sinusoidal current. It only remains to couple the apparatus to a miniature radiating system, preferably :iided by a mirror reflector, to send the waves as a pencil in the direction required. .. . J