WIRELESS NEWS.

Press, Volume LIX, Issue 17749, 28 April 1923, Page 11

WIRELESS NEWS.

INDUCTANCES AS USED IN RECEIVING CIRCUITS. VARIABLE AND FIXED TUNING COILS. (spbcmllt warmssr tcb "ihb psbss.") ■ (By "Electra.") The frequency of the oscillating currents which n-ill flow in an oscillatory circuit, and therefore the wave-length which can be received by it, is a function of the capacity and inductance of the circuit. In order that wireless messages can be received, the receiving circuit must be tuned to the wave-length of the incoming oscillations. The wavelength of a circuit can be conveniently adjusted by varying the value of the inductance. Broadly speaking, inductions can be made inw two classes: Variable inductances—fixed induct, ances. 'Variable inductances are used when comparatively small adjustments of tuning are required. Fixed inductances are generally employed to be added to the circuit when a fairly large alteration in wave-leugth is to be made. Thus a set of interchangeable fixed inductances may be provided for approximate tuning ou various wave-leugtns, hnal close adjustments being made by aitaus of a variable lnuucumce.

The Variable Type. Variable inductances may be of either tke aimer, or voi-iuiiieier typtis. aiiuer •muucwuices consist ol a *ayer co.i, a narrow senp oi wire aioug oue whoiu >eugtn of tne coil being oareu so tuat connexion may be made at any point by a contact, wliich can oe moved along uie coil. Very accurate adjustments can be made on such a coil, the minimum variation being the value of the'inductance of one turn. A smiaar sensitive adjustment be obtained on a tapped inductance, i.e., a coil from wnich connexions are brought out at intervals along its lengtn to a radial switch having a stud for each tapping. The usual method of taking the tappings off is to tap the first'ten turns, bringing each.off to a separate stud, and then divide the remainder of the coil into nine parts, and bring a tap out from «ach of these to a separate lot of studs. This will make two switches with ten studs to each, and it will be found that exceptionally fine tuning is obtainable with this arrangement. A less Eensitive adjustment can be obtained on a coil that is only, tapped, say, every ten turns, .and therefore in this case only uses one switch. The practical limit to the number of contacts on such a switch is about 20, this corresponding to a 5 per cent, variation.

Fin© Adjustments. By far the most accurate adjustments •are possible in the variometer type of inductance. - In these part of the coil is fixed, and the remainder made to revolve within the fixed portion. When the currents in the two portions are circulating in the same direction, the total inductance is equal to the sum of the inductances of the two parts. If the moving portion be rotnted through •an agle of Iso degrees, the fields of ttie ..two.,coils are in opposition, and the total inductance is equal.to the deference' between the inductances of the two parts. These are-the maximum and minimum values, and between these limits extremely fine adjustments can be made. • Fixed Inductances. Inductances of fixed value may be classified according to the method or winding the coil. The eingle layer coil is undoubtedly the most emcient type. Unfortunately this type of coil becomes very unwieldy if designed for long wave-lengths, the practical limit being about 6IXH) meters. The expedient of winding the coil in two or more layers introduces the disadvantage that the. potential difference between the two layers is so great that the coil has quite an appreciable capacity, and this distributed condenser effect results in decreased signal strength. _. Various alternative methods of winding have been devised to reduce the size of the coil, and to avoid the selfcapacity. Of these, the simplest in~3esign, but not the easiest to construct, are those coils in which the turns are wound on top of each other in such a way .that the potential .difference between _ layers and between adjacent turns is a minimum. Other forms, as, for example, "basket" coils, are arranged with the windings zig-zagged around the .circumference of the coil in such a way that the conductors cross each other at right angles. The "honey-comb" duo lateral, and Burndept ooils are variations of this type, and are successful in reducing selfcapacity to practically negligible values. American Amateur Eeception. Following are the calls received by Mi* L. bdaue, of I'imaru, since December 7th —calls' received previous to haul uate srere published in last Saturday's "Press":)--

December 7th BZY, 7.12 p.m.—BZY to OQ, 7.27.—6Z1 to CQ, 7.37, 7.39, and 7.43 p.m.—6251 to OQ east, 7.46 and ?.49 p.m. December 10th—6AVD to CQ, 7.50 p.m. December 16th—6JD to CQ, 10.12 p.m. —6JD to SPX, 10.13. December 17th—6KV—«ZND—6ANH—6AWP (on 5 watts)—9BED. December 19th—6ZMI—7SC to CQ, 8.45—6JD to CQ—6PD, 9.44 p.m. December 20th—9GK to CQ, 11.21 p.m. again at 11.32 p.m. December 21st—78C to CQ, 7.47 6AWP to CQ, 7.54 p.m.—7SC, to &QR, 8.14, 8.15, and 8.17 p.m.—6ANH to 9DQM, 8.141 —7GS to SGR, 8.27 p.m.—<6Z.fc,9.5 p.m.—9GK to CQ, 9.7 p.m—! 9ARB to BCF, 9.20 p.m. December 22nd—6BUN, 10.16 p.m.— 6BUN to SZAV, 10.21, 10.32 9BSG to CQ, 10.48. December 24th—6JD to CQ, 11.9—61F to 80WP, 11.12 p.m.—6JD to 9BP, 11.32—G1F to 9AMB, 11.38, 11.32, 11.49—61F to 9BP, 11.44 p.m.—6lF to CQ, 11.57 p.m. December 28th—9YAG to BGV, 8.3 p.m.—9YAG, 8.14, 8.26, 8.30, 8.36, - and 3.45. ' December 31st-«KA. 10;0, m 5, 10.11, 10.18, 10.24, 10.34. p.m., 12.5, 12.9, 12.14 a.m. The calls for January will be printed in next Saturday's "Press."

TJ.S. Amateur Radio Districts. It may be of interest to those who are following up the reception of American amateurs, and aro unable to procure an American Call Book, to have the various U.S. ltadio Districts enumerated. Districts 1, 2, 3, ana 4 are on tho Atlantic side, and districts 6 and 7 on the Pacific side. Number 5 district takes in most of the southern central States, one boundary being the Gulf of Mexico. District No. 8 is on the Eastern side of the Great Lakes, and takes iu part of the States of .Michigan,' New York, Pennsylvania, and all of West Virginia and J)hiq. Number 9 district covers the Northern Central States and part of the Lakes. The four States on the southern bonndKry of this distmt are Colo--ado, Kansas, Missouri, and Kentucky. Number 0 district, where most of the calls received have come from, is made up of four Slates in the south-western.

corner of the U.S.A., namely, C*i fornia, Arizona, Utah, and Nevada. ! ■ •, . ' Questions. "Enquirer."—l will write on t subject of high and low resistan pnoues in next Saturday's "Press," at present there 4s a lot of controver f on this subject. g "G.H.T.T., Opawa."—A loose coupl ] suitable for tuning up to 600 metr I may be made as follows:—The prima j should be a tube 3iin in diamet | wound with about 100 turns No. ! 1 DCC. The secondary should be worn on n tube that will just slide with; the primary and should have about 1! turns No. 80 DCC, both primary ai <! secondary to be tapped. ;j Questions t ill be answered in th; : column on matters pertaining toWili less. All letters must be addressed -1 the "Electro," c.o. Editor, , "Ti Press," and must reach this office fc fore 12 o'clock on Monday. Name aji address must bo given on all letter tind only one side of the paper writtel on. I

GisDorno Badiopnona. ', It has become quite a habit' here no' to eitUer tune in to Uisbomo or 6ha valley, for tuere is no doubt that the are both very U.S.A., and with three c tour valves on, wen, it is like a grume phone. Mr i\ it. btevens, of Gisboraj is a real hard boiled ".Hani," an knows exactly what the feeling is whe the clock strikes 1 a.m A word aboti his transmitter should be of interes to all Canterbury "bugs." Mr Stevens is at present using 3-< watt radiotrons and modulating al grids. The generator is a one, and gives off varying voltagei from 600 to 1600 volts. The plates o) the tubes are a dull red when the sei

is working. The aerial is 60ft high 140 ft long, 5 wire "T" type. ' Tht counterpoise, which is used alone, is o1 the tuned type. The radiatron is approxi mately 1.8 amps. The counterpoise' ii directly underneath the aerial, and is made up of 30 single wires about 1{ inches apart and Bft above the ground; Mr Stevens has tried out various cir* cuits with varying degrees of but the best so far and the one ia , use at the present time is to be found on page 10S0, December issue, 6( "Radio News." There is one feature of the receiving set that is worthy of uote, and that is, that Myres tubes are used. The circuit is of the. usual typi in everyday use, but according to W dtevens it is the tubes that do the trick. I can not do better than quote Mr Stevens'B own words in reference' do these tubes:— ''l use Myers tubes! and they're great, they root the devil out of sight. VIS can be heard and read at 100 yards easily, and it is ab- I -solutely impossible to wear phones oil VLD, VLC, VLW, or VLA, etc. to Yank amateurs; 6ANH and 9DOK, aiul' many others are copied, also' what I ; take to be a Yank Broadcaster can"'.W heard nearly every eyening about .<s'. : &U ' p.m.; he has rather a bubbling carrier wave, and I have heard snatcnetfof music from him.. I must state, thai if] in conjunction with the above tuner* « I have three stage audio, frequency'f hanging on the end of her, and rarely '% work without it. I root up part come*/1 by the use.of the C battery, and also,': having the first transformer with a' tapped primary. This makes a very" big difference, when transformers howl on a certain wave-length by changing.' the ratio of the first, transformer the' howl ceases, and I can tell you they" are some signals the little Myres make*.l Before I took to Myers I used the A P I tub o for detector and French R fori A.F. I have made an offer to' the" amateurs here, that if any ; of them 1 can wear the-phones for five minute* ; I will make them a present of a Myres'' and holder So far no one has" succeeded, and I myself have injured one' of mylars slightly through happenm K to have the phones on when a local; station opened up. NPM and NPN can be heard away down the street at: times. I mnst stqto that these re,"' suits are chiefly accomplished by the' *v °V ? After reading.; this, it's O batteries and Myres tubes, for me, I guess.'