RADIO

Star (Christchurch), Volume XLIV, Issue 164, 13 July 1931, Page 4

RADIO

y (By

"AERIAL.")

LOCATING INTERNAL NOISES IN RECEIVERS. Th.e Best Indicator. The best instrument which can be employed as an indicator of noise is a good speaker or headset, because, in the last analysis, what you hear is what counts. It is of the utmost importance. however, that the speaker or headset be in good mechanical condition. The most frequent sources of noise are varying resistors, intermittent contacts or shorts. An ohmmeter and continuity tester arc frequently of great assistance in detecting these. Intermittent contacts can be quickly established by using the continuity tester. This consists of a voltmeter connected in series with a 41-volt “C” battery. When the two test leads are connected across the terminals of the resistor or the apparatus under test it will read less than 41 volts. If the meter needle flickers between certain values it indicates a varying resistance and that part of the circuit should be most carefully checked. In checking the condition of resistors do not bear down on the resistance, but pull up with your test leads. This wifi serve to strain the connection and if an intermittent contact is being made it will show up when making this test. Stage By Stage Elimination. If it is determined that the noise is internal it is necessary to locate the particular circuit which is causing the trouble, namely, whether it is in the audio or radio frequency system, the detector or power pack and in whicli particular stage the trouble arises. The best method to follow here is the stage by stage elimination process. In this method one stage is added at a time and observation made when the noise comes in. All valves should be kept in operation. This method of test assumes that the aerial and ground system is in perfect mechanical condition and that it is not itself a source of noise. Assume now that the noise is internal. Therefore disconnect the aerial and ground. The noise should still be present. Then short circuit the grid or grids of the output valves. This immediately disconnects all valves ahead of t.he output valve or valves. If noise is still present it means that the source of trouble is in the output stage or in the vol’tage supply or the speaker and these should be examined carefully. If noise is not present the output stage and voltage supply for these valves is O.K. Now add the first audio frequency stage by disconnecting the I short on the grid of the output valves. 1 JBhort circuit the grid of the first r.f. valve. If noise comes in now it is in the first audio frequency stage or voltage supply to this stage. These circuits should be critically examined. If noise is still absent, both these stages and their associated voltage supplies are O.K. Next remove the short circuit from the first audio frequency stage and short circuit the detecCbr grid. Proceed this way until the source of trouble :s definitely lo<;tt<d in :i particular circuit. Knowing the circuit in which the trouble is present, it is a simple matter to make coxrections. When each radio frequency stage is checked and the grid of each radio frequency stage is shorted, rotate the variable condenser to see whether this introduces noise. Frequently the variable condenser plates may short at some point and cause noise. This test should be made with each radio frequency stage shorted sc as to determine which particular variable condenser is causing the trouble, ii any. Visual Inspection. Keen visual inspection is one of the simplest and most effective means available for use in locating ordinary sources of noise. In this method nc instruments, other than the eyes, are needed, bur one must exercise one’s powers of observation. A visual examination of tha wiring of the set will show connections which are loose of unsoldered, soldered pnin« which are corroded

tured or mechanically Injured, valve socket prongs which are bent and make imperfect contact and so on. The possible sources of trouble causing noise which can be detected by the observant eye are many. One of the first steps to lie taken, therefore, is to examine critically the wiring and construction to see what defects can be found. TO-NIGHT’S CONCERTS. Following are the wireless programmes to be broadcast to-night:— 2YA, ’Wellington (416 m 7.0: News session. S.O: Overture, Berlin State Opera Orchestra, “ Italiana in Algeria” (Rossini). 8.9: Baritone, Mr Val Jones, “I Love You More,” “So Fair a Flower.” 8.15: Musical portrait series, " Russian Music ” —Trio, Madame Evelyn de Mauny, Mr Leon do Mauny and Mr Claude Tanner. “ Trio in D Minor” (Ist Movement—Allegro Moderato); violin and piano, Mr and Madame de Mauny, “ Andante ” from “ Sonata in D” (Cui). 8.29: Soprano, Madame Dorothy Cronin, " Mobil Signor," “ Love lias Eyes,” “ The Cloths of Heaven.” 5.39: Organ, Leo Stin, “ Peer Gynt ” (Greig), “Morning,” “Death of Ase.” 8.40: Contralto, Miss Evelyn Robinson, “ Madrigal,” “ Silent Moon.” 8-52: Orchestrina, “In the Silence of the Night ” (Rachmaninoff), “ Serenade.” 9.0: Weather forecast. 9.2: Berlin State Opera Chorus and Orchestra. “ Carmen Ballet—Music and Introduction to Act 4” (Bizet). 9.10: Madame Cronin. “ 'Twas in the Golden Time of Spring,” “ Slow. Horses. Slow,” “ Scythe Song.” 9.19: Trio, “Andante Con Moto and Finale” (from “Trio in C Minor”) (Mendelssohn). 9.24: Mr Jones, “Loving Smile of Sister Kind,” “ Nelson’s Gone A-Salling.” 9.40: Organ, Leo Stin, “Peer Gynt Suite” (Greig), “ Anitra’s Dance,” “Solveig’s Song.” 9.4 G: Miss Robinson, “ The Bitterness of Love.” “The Sea Hath Its Pearls.” 9.51: Singing Teachers’ Society. “ Brothers, Your Hands.” 9.54: Orchestrina, “ Valse Triste ” (Sibelius), "From Foreign Parts” (Moszkowski). 10.0: Dance programme—Foxtrots. “ Vamos A 1 Merendon,” “ First the Right Leg.” “ A Very Good Chum.” 10.9: Waltz, “ You’ve Been My Lucky Star”; foxtrots, “Just You.” “Both You and Myself.” 10.18: Vocal. Jack O'Hagan. “ Rambling Down the Roadway.” 10.21: Tangos, “Alla Va El Caldo,” “La Voz Del Viento,” “Amarguera”; waltz, “Good-bye.” 10.30: Foxtrots, “To Begin With a Big Question Mark.” “ Hello Sweet Lady," “My Heart is Longing for You.” 10.39: Vocal. Jack O’Hagan. “With My Guitar and You.” 10.42: Tangos, “ Nubes de Jfumo,” "The Tale of Good Fortune,” “ Soledad.” 10.51: Foxtrots, " Bombel'os,” “Mi Perrito.” 11.0: Close. 3YA, Christchurch (306m.—930k.). 7.0: News session. 7.30: Dialogue. Messrs E. E. Wiltshire and F. C. Fair-

tinued). 8.6: Band programme by New Brighton Municipal Band and assisting 3YA artists—Band, “Majestic” (Teasdale), “ W r e All Go-o-o Ha! Ha! Together” (Harrington). S.S: Tenor. Mr Adam S. Mitchell, “Maiden Mine,” “The Captain’s Ditty.” 5.14: Banjo, Harry Reser, “Cracker Jack,” “ Flapperette ” 8.20: Mezzo-contralto. Mrs Sen Jowott. “In Springtime,” “Morning and You.” 8.25: Band. “ Moonlight on the Colorado" (Campbell). 8.32: Humorous recitation. Mr Denys Cow, “ With the Photographer.” 8.43: Accordeon, Michel Haling, “ Mya Valse,” “La Mitrailleuse.” 8.49: Baritone, Mr Percy Caithness, “ Inter Nos,” “ Just a Cottage Small.” 8.53: Band, “Bathing in the Sunshine” (Nieholls), “Three Little Words" (Ruby). 9.1: Weather report. 9.3: Rumanian Gypsy Orchestra. “ L:i Bar kon ” (Rumanian song). 9.6: Mr Mitchell, “True Till Death.” 9.12: Band. “Musical Fragments” (Dimmer). 9.2<): Mrs Jowett, “ TTusheen,”'“ For liver and a Day.” 9.25: Grinzing Sehrammel Trio, “Gay and Jolly,” “Jolly Alpine Larks.” 9.31: Mr Cow, “"Wrongly Attributed.” 9.36: Band. “My Sunshine Came on a Rainy Day,” “Sing Something Simple.” 9.4 4: Mr Caithness, V Loch Lornond and You,” “ A Wee Hoose Mang the Heather." 9.49: The Jolly Old Fellows. Drihking Songs.” I 9.55: Band, “The Toilers” (Francis). I 10.1 : Close.