454 



Popular Science Moidldy 



Receiving Long Waves 



F. F. L., New Rochelle, N. \'., writes: 



Q. I. I have an aerial of the inverted "L" 

 type, consisting of four wires spaced 2 J feet 

 apart. It is 5S feet in len§;th, 50 feet in height 

 at one end and 35 feet at the lower end. The 

 lead-in is attached to the lower end and is 12 feet 

 in length. The ground wire is 40 feet in length. 

 The primary winding of the receiving trans- 

 former is wound with 255 turns of No. 24 S.S.C. 

 wire on a cardboard tube 3J" in diameter. 

 The secondary winding is made on a tube 

 3J" in diameter for a length of 5j" with No. 

 30 S.S.C. wire. There are eleven taps on the 

 primary winding. I use an Audion detector. 

 Can you compute the wave length of the aerial 

 and the possible adjustment with the receiving 

 tuner described? 



A. I. The natural wave length of the aerial 

 system is approximately 190 meters, and with the 

 primary w inding connected in series is adjustable 

 to 1900 meters. The secondary winding with a 

 capacity of .0001 microfarads in shunt will 

 respond to 1600 meters and to about 3,000 

 meters with .0005 microfarads in shunt. 



Q. 2. Can this antenna be loaded by means of 

 inductance coils to receive Naucn, Germany, and 

 allow the reception of their signals day and night 

 with a sensitive oscillating audion? It is im- 

 possible to erect another aerial. 



A. 2. It would be possible to load this aerial 

 so as to secure response from Naucn, Germany, 

 but the present receiving tuner will not aflford 

 sufficient closeness of coupling for the best re- 

 sponse. You should construct apparatus like 

 that described by A. J. Watts in the November, 



1915, issue of the Popular Science Monthly. 

 Also see the article by McKnight in the April, 



1916, issue. 



Q. 3. When using loi turns of the primary 

 winding, and five- sections of the secondary 

 winding, with a correspondingly low degree of 

 coupling, i obtained signals from the Brooklyn 

 Navy Yard loud enough to be heard over two 

 floors. When the entire primary and secondary 

 windings are in use wit ha dose degree of coupling, 

 I get .Arlington signals loud enough to hear 

 them 20 feet from the head telephones. I also 

 receive Brooklyn Navy Yard at this point just as 

 loud as at the first mentioned adjustment co[n- 

 pletely drowning out .Xrlington. A change in the 

 coupling or an altenilion in the capacity of the 

 variable con<lenser has the effect of weakening 

 the signals from Arlington without a decrease in 

 the strength of the signals received from the 

 Navy Yard. 



I exix'rienced similar results with New 

 York Herald and the Cape Cod, Mass., stations. 

 Previous to this I owned a transformer with 

 which I could cut out the New \'<)rk Herald and 

 still receive Cape Cod, but diil not get any 



stations as loud as those I can tune to with the 

 present coupler. I also hear signals with this 

 coupler that before could not be heard. I have 

 tested the windings carefully for short circuits: 

 do you think the phenomenon I have described 

 is due to faulty construction or what is the cause 

 of it? 



A. 3. You will readily understand from the 

 data we have given you that your receiving tuner 

 cannot be placed in resonance with Arlington, 

 although with a close degree of coupling you are 

 able to hear these signals on account of forced 

 oscillations. You should also understand that 

 when a close degree of coupling is used between 

 the primary and the secondary winding of a re- 

 ceiving tuner that the receiving circuits are 

 broadly tuned and simultaneously responsive to 

 a number of wave lengths. To place your ap- 

 paratus in complete resonance with Arlington 

 you require larger primary and secondary wind- 

 ings, or a load coil and larger secondary con- 

 denser. 



Q. 4. Are the results obtained just as satis- 

 factory when the primary winding is tapped 

 every twenty turns and the variometer connected 

 in series with the antenna circuit as with the 

 ordinary method where two switches are em- 

 ployed for the purpose? 



A. 4. Yes, it is somewhat better to use the 

 variometer, as a rule. 



The Construction of Variometer 



Windings in Single Laj'ers 



and in Multi-Layers • 



M. A., New York, N. Y., inquires: 



Q. I. In the construction of variometer coils, 

 should they be wound in single layers or in multi- 

 layers? 



A. I. If the coils are narrow and consist of 

 but a few turns, it is practical to use a multi- 

 layered winding, but if the variometer is to con- 

 sist of a great number of turns of wire, multi- 

 layered winding should be avoided. 



Requirements of Fire Underwriters 

 Concerning Radio Installations 



G. S., Richmond Hill, N. Y., inquires: 



Q. I. I am somewhat confused on the re- 

 quirements of the I'ire Underwriters in respect 

 to radio inst.illalions. What are the dimensions 

 of the lightning switch and the size for the corre- 

 sponding earth wire? Can copper clad iron wire 

 be used in place of copper wire? 



A. I. The lightning switch must have a cur- 

 rent carrying capacity of 100 amperes and the 

 ground wire nuist be at least a No. 4 copper 

 wire. Iron wire of any description will not be 

 passed. 



