WIRELESS NEWS

Press, Volume LXVI, Issue 20104, 6 December 1930, Page 23

WIRELESS NEWS

(By "MAX.") The dynamic speaker dates back some years and is not an absolutely new development, ns many may imagine. Tho Magnavox firm hold the lirst patent covering tho principle of construction used in all moving coil loudspeakers. The writer remembers reading a full description, in a copy of "Radio News," some five years or so ago, of how to make a moving coil unit. Sinco then there have been modifications making for improved types, especially in regard to the shape of tho pole picoes and the moving coil itself. . , ... Picture to yourselt an iron pot with very thick walls, etc., and with a close fitting lid beourely screwed t>o■ it. Imagine a hole of perhaps an JP°h diameter in the centre of the lid and Hush with the outeide surface of the lid is the end of an iron rod which is just a fraction of an inch smaller in diameter than the opening through whic-li it projects. Tins rod extends right down the centre of the pot, being secured to the bottom. Around this rod is a bobbin of wiref either coarse or fine, depending upon whether it is to oarrv a large current driven bv a low voltage or vice versa. "Tho whole makes up an electromagnet of special shape so that a htriTnii magnetic field is created across the outer end of the rod and the circumference of the lid immediately surrounding it,. Now a very thin coil of tine wire Gts in the space between the rod end and the hole in the lid. but it must not touch either. This coil is carefully suspended and is attached to a stiff paper cone, which it actuates when varying currents from tlie radio set are passed through it. Under working conditions the fine c.-oil moves back and forth in the mairnetic field across the iron rod and tho lid. Now when an alternating current passes through ' the coil, it sets up a corresponding magnetic field of its own which is at one moment working with the steady field of the pot magnet and the next fraction of a second is working against it, being drawn further into the gap, as the space is called in which the coil is suspended, in the first instance and pushed outwards in the second case. This action, by a lever system, vibrates the cono at speech frequencies. As the pull of a magnet upon a separate piece of iron, for example, varies inversely as the square of the distance, it is obvious that as small a gap as can possibly be used should exist and this necessitates a coil of very fine wire. A certain balance has to be maintained between tho requirements of both theory and practice, but these points are outside of the mere principles of operation of a moving coil speaker and will not be pursued here. One of the main features of this typo of speaker is that a very intense magnetic field can be set up with an elec-tro-magnetic system, very much greater than that obtainable from permanent magnets. Therefore tho moving coil operatos in a strong field and can deliver a large output. However, as was stated in this column when considering some of the exhibits at tho recent Radio Olympia in Kncland, steady improvements have boon made in the dfcvelopment of special stoel for permanent magnets, thus enabling stronger magnets to he manufactured for a given size of magnet. •* * At a recent meeting of the Radio Society of Christchurch, the subject for tbo lecture and demonstration was magnetism, and t"he different ways of developing magnetic forces were both described and shown. Th© fact that a simple copper wire can se>t up a magnetic field about itself when a current is sent through was proved by means of iron filings and a battery. This experiment can be performed at home by anyone who has an accumulator of the car kind available. Just connect up a p\ece of copper wire so that it passes vertically through a stiff piece of cardboard and has the two ends joined to tho battery terminals through a switch. Sprinkle fine iron filings around the wire where it enters the cardboard, and then gently jar them after switching on the current. The object of the switch is to enable the circuit to bo made and broken quickly as a heavy current is drawn unless a re : sistance of a few ohms is inserted. As soon as the filings arrange themselves in a pattern when jarred, cut off the electricity. * # An excellent elcctro-magnet can be made by procuring a bolt of soft iron and placing it in a coal fire and leaving it there to cool down very slowly as tho fire dies out. Now wind on some medium gauge insulated copper until the outer diameter of the coil is about fwice the diameter of the bolt. Connect the two ends of the winding to a battery and übo filings as before. The electro-magnet should be tried in different positions just beneath the cardboard, end on for example, and lying flat. The form taken by the filings when jarred shows the lines of magnetic force. A discarded car coil will serve also, as will an ordinary electric bell if the trembler is screwed up tightly.

An Australian correspondent states that he has recorded the signals from over 500 short wave stations, and has received cards from the station operators. The average amateur is rather deluged, at times, with requests from listeners who are card-hunting, and this accounts for many requests beiDg consigned to the waste-paper basket. Amateur cards are termed ''QSL" cards, meaning cards confirming two-way communication. Many of our readers will have seen samples at tho last radio show in Christchurch, at the amateurs stan'd. * * Tho electron is a constituent of nil kinds of atoms and when any are added to or removed from an atom a condition of electrical strain ■_ exists, for electrons are negative particles of electricity and exactly balance the remainder of an atom which is positive. If electrons are in motion as the effect of chemical action, or the movement of copper coils of wire, as in a generaltor, we have a current of electricity, but when there is ' an accumulation as a result of friction, as happens sometimes with a running belt in machinery, a stationary charge, called a static charge, is formed. This occurs also in clouds, probably as a result of the effects of the sun s rays, and if the electrical potential or voltage is built up enough it might brca>ncross to some other object or cloud of different electrical tension and a spark is formed. Between clouds or between a cloud and the earth a large flash occurs and the sudden collision between thu tremendous stream of electrons and the molecules of air sets the latter into heavy oscillations and v,c have thunder. Eather a curious fault has been "hen to the writer to unravel. It is in a newly-bought, cheap one-valve receiver which functions after a fashion when the "A" battery only is connected but utterly fails to record a sound when the "13" battery is in circuifc and it makes no difference which wav it is joined up, it being thought that perhaps the terminals were wrongly marked. Just ponder over the possible causes and when the fault

Notes From Far and. Neav

BROADCASTING. TO-DAY'S PROGRAMMES. 3YA, CHRISTCHUUCH (980 Kilocycles.) i P ' m 'j 0 - Afie J Qoou session—Gramophone recital. . Sports results. 6.0: Children s hour Aunt Pat, Sunny Jim, and Jack Irost. 6.0: Dinner session. 7.0: Ne*s session. 7.30: fclporta results. 8.0; Chimes. A audeville and Dance Programme. Overture —Regal Cinema Orchestra, "Show of Shows Selection. 8.8: Baritone—Mr Clive Kindle, Spanish Gold" (Howard-Kisher). 8.12: Saxophone—Frank Ferrera and John p. Paaluhi, "Kilima" (tradtl.). 8.15: Humour —Mr J. J. Flewellen, "The Sceneshifter's Lament" (Anon). 8.20: Instrumental—Studio Octet (Conductor, Harold Bock) Lustspiel Overture" (Kela Bela). 8.27: Soprano—Miss Hilda Hutt, (a) "Sleep and the Roses" (Tate); (b) "Stay With Me, Summer" (G. Morris). 8.32: Accordion Airs G. Amer, (a) "Peggy O'Neill" (own arrangement); (b) "Mother Machree" : (c) 4 'lrish Jig." 8.37: Novelty—The Two Gilberts, (a) "Smith's Crisp Crisps" (Woston Lee); (b) "Where the Sweet For-get-me-nots Remember." 8.43: Humour in song—Mr George Titchener, "We're Uncomfortable." 8.48: Studio Octet—Musical comedy selection, "Sally" (Kern). 8.58: Weather report and station notices. 9.0: Novelty liegal Pantomime and Company, "Dick Whittiugton." 9.12: Baritone—Mr Clive Hindle, (a) "The Fishermen of TCnglaud" Phillips); (b) "At Tankerton Inn" (Howard Fisher). 9.18: Studio Octet, (a) "Andantino" (Lemarc); (b) "Hungarian Dance." 0.28: Humour—Mr J. J. Flewellen, "The Laundry Problem" (Leucock). 9.33: Soprano—Miss Hilda Hutt, "Love's a Merchant" (Carew). 9.38: Studio Octet, (a) "Magic of Love" (Yani*); (b) "Aubado Priataniere." 0.46: Acrordion —Mra G. Amor, (a) "Blowing Bubbles" (own arrangement) ; (b) "Three Troublos" (own arrangement). 9.51: Coster love and humour in song—Mr George Titchener, (a) "My Old Dutch" (Chevalier); (b) "Mary Kllen" (Haines). 9.57: Jazz Waltz—Studio Octet. "All Alone" (Stothart). 10.1: Dance music until 11 p.m. 32C, CHRISTCHURCH (250 Metres.) 10.0 a.m.: Women's session — 1 'Wedding of the Winds," waltzes, American Symphony Orchestra. 10 5; Tested incipos. 10.25: "La Mariposa," Fran?. Falkenhurg (piano): "The Radiance in Your Kyes," Marie Jiappold (soprano); ''Serenade Espagnole," Albert Spalding (violin); "Ukulele Lady," Eddie Peabody (banjo) ; "Paradise," Paul Reimers (tenor); "Monastery Bells," United States Marine Band. 11.0 a.m.: "Op the High Alps," Venetian Instrumental Quartet; "Balmoniathor," Franz Falkenburg (piano); "Mighty Like a Rose," Marie Tiffany (soprano); "Prelude," "Le Deluge," Albert Spalding (violin); "Let It Rain, Let It Pour," Eddie Peabody (barj.io); "Dream Faces," Thomas Chalmers (bari"Vesper Bells at Kve," Sodero's Band. 11.30 a.m.: Close down. 2VA, WELLINGTON (720 Kilocycles.) 3 p.m.: Chimes. Selected studio items. 3.30 and 4.30: rcsulta to hand. 5.0: Children's seshion. (5.0: Dinner session. 7.0: Kewß sessiou, market roports and sports results. 8.0: Chimes. Overture—Salon Orchestra (Conductor, Mr M. T. Dixon), Selection of "Guy d'Hardelot's Songs" (arrgd. Higgs). Selection —Salon Orchestra, ''llyde Park Suito" (Jalowicz). 8.16: Quartet — The Lyric, "Honey, 1 Wants Ycr Now" (Coe). Tenor—Mr Chas Williams, ''The Gay Highway" ( Drummond ). Soprano— Miss Phyllis Lcighton, (a) "Here's to Lovo and Laughter" (Rubens); (b) "Deep Night" (Henderson). Humour—Mr Len Ashton, (a) 'Nobody" (Anon); (b) "Tale of a Guinea Pig" (Gideon). 8.32: Guitar band—Mrs Mildred Kenny's Guitar Band, (a) "Around the Corner" (Kasscl-Kahn) ; (b) "Hawaiian Islands Waltz" (SmithCuzenza) ; (c) "Melc Hula*' (Clarke) ; (d) "Beauteous Isle." 8.44: Quartet —The Lyric "MyKterious Mose" (Doyle). Tenor—Mr Roy Hill, "Joy of Life" (Corbett). Popular songs—Gibson and Standen, (a) "If I Had a Girl Like You" (McDermott); (b) "Telling it to the Daisies" (Warren). Negro part song —Lyric Quartet, "Swing Along" (Cook). 8.59: Weather report and station notices. 9.0: Arthur Pryor's Hand, (h) ''Th.j Whistler and His Dog" (Pryor); (b) "'1 he Warbler's Serenade" (Perry). Guitar—Roy Sraeck and Art Kahn, "Itchin' Fingers'' (Robiaon). 9.12: Baritone —Mr W. Goudie, "Ne'er do Well" (Tate). Song and quar-tet-—Mr W. Binet Brown and Lyric Quartet; "When You Played the Organ" (arrgd. Gatheridge). Humour —Mr Len Ashton, (a) "The Pink Plant Pot" < Handlcy ) : (b) "Nowt" (Handley). Selection—Salon Orchestra, "Request Item." Novelty—Salon Orchestra, (a) "Reconciliation" (Fletcher); (b) "Pirouette" (Finck). 9.39: Soprano— Miss Plivnis Leighton, (a) "I Know My Love" (Hughes); (b) "The Oak and the Asfc" (Traditional). Popular songs—Gibson and (L'tanden, (a) "Somebody Mighty Like You" (Ward); (b) "I'm Sailing on a Sunbeam" (Dreyer-Macdonald). 9.50: Instrumental —Salon Orchestra, "Dance Novelties." 10.0: Dance programme. IYA, AUCKLAND (900 Kilocycles.) 3 p.m.: Afternoon session—Selected studio items, including literary selection by the Announcer. 5.0: Children's session, conducted by Cinderella. 0.0: Dinner Kession. 7.0: News and market reports. 7.40: Talk— Mr A. K. McMahon, "Chrysanthemums." 8.0: Chimes. Overture —Band of H.M. Coldstream Guards, "A Musical Switch." Selection—Band of lI.M. Coldstream Guard?, "H.M.S Pinafore." 8.17: Baritone—Mr Peter Davidson, (a) "Listenin' " (Wood); (b) "Muleteer of Malaga" (Trotero) ; (c) "Before the Dawn" (Lang); (d) "Salaam" (Lang). 8.27: March——Orchestral Octet, under direction of Mr Harold Baxter, "Wellington" (Zehle) ; orchestral. "Fantastic Gavotte" (Spaight). 8.37: Soprano—Miss Chrissie Foster, (a) "Peter Pan" (Henderson); (b) "There's a Little Green Cabin" (Forster); (c) "The Little Dutch Tile" (Adams). 8.47: Selection —Orchestral Octet, "Katinka" (Friml) ; waltz. "Elfentanz." 9.1: Evening weather forecast and announcements. 9.3: Novelty—"A Miniature Concert." Vocal jazz—The Duncan Sisters, "Hoosier Hop" (Dreyer-MacDonald). 9.14: Novelty —The Neiafu Duo, (a) "Laughing Eyes" (Davis); (b) "On the Beach at Waikiki" (Kailimai); (c) "Hear the Ukuleles ACalling You" (Scott); (d) "Wai o Minehaha" (Waialeale). 9.27: Orchestral Octet Ballet Suite, (Finck), (a) "Pas do Deux"; (b) "Pas Soul"; (c) "Ensemble Finale." 9.39: Contralto—Mrs B. Jellard, (a) "The Carnival" (Molloy) ; (b) "Ring Bells, Ring" (Day); (c) "Love and I Wfcut Down tho Dale." 9.49 Violin—Mr Harold Baxter, "Romance" (Juon). Two small pieces—Orchestral Octet, (a) "Melody in F" (Rubinstein); (b) "Moment Musicale" (Schubert). 9.59: Programme of Dance Music from the Studio. 4TA, DUNEDIN (650 Kilocycles.) ;; p.m.: Chimes. Selected gramophone items. 4.25: 'Sporting results. 5.0: Cbildren'w hour, conducted by Undo Sambo. 6.0: Dinner music. 7.0: News session. 8.0: Chiniej. Marches—Black Diamond Band, "Old Comrades" (Teike) ; "Fatinitza" (Suppe). 8.7: Special programme reminiscent of tho "Jubilee Singers." Solos, quartets, and chorus as performed by the original Jubilee Singers, being a company of emancipated plaves which toured the world forty years Hgo, presented hy the Choir of S»*t. Stephen's Presbyterian Chureb, under direction of. Mr B. Rawlinson. Chorus—The Choir, (a) "Go Ring Dem Bella" (traditional); (b) "Steal Away (traditional). Quartet- —Choir, "Camptown Races" (traditional). Tango—Marimba Centro Americaua, "Aguar* Dormides" (Bolanos); "Morales Lopes" (Bolnnos). Soprano——"Wasn't That a Wide River?" (traditional). Chorus—"Stand the Storm" (traditional). .Violin—Miss Eva Judd, (a) "First Mazurka" (Heutey; (b) "Songs My Mother Taught Me" (Dvorak-Kreikler). Quartet —"Kemo, Kimo" (traditional). Banjo -—Joe Brannelly, "Eccentric" (Robiuson). Solo —"Nobody Knows tho Trouble" (traditional). Chorus—"Ain't Got Weary Yet" (traditional). Marimba —Mr Hugh Dalziel, "Dance of the Raindrops" (Leproy). Solo —"Were You There?" (traditional). Chorus "My Good Lord's a Been Here" (traditional). 9.0: Weather report and station notices. 9.2: Novelty Orchestra, "Danse Bagatelle" (Burdon); "Ginger Snaps." Quartet —"The Old Cabin Home": solo, "Go Down. Moses" (traditional). Violin—Miss Eva Judd, "Acs Wien" (Kroisler). Chorus (a) "I'm a-liolling; (b) "Lord, What a Morning" (traditional). Piano—Raie da Costa, "High Society Blues" (Hanley). Quartet —"Who's Dat Calling" (traditional). Solo—"Carry Me Back to Old Virginny" (traditional). Marimbaphone—Mr Hugh Dalziel, (a) "Waldmere" (Losey) ; (b) "Sleepy Valley" (Hanley). Chorus "Prepare Me", (traditional). Solo—"Swing Low, Sweet Chariot" (traditional). New Mayfair Orchestra, "Sir Roger de Coverley" (Daykins). 10.0: Dance session.