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Page:Popular Science Monthly Volume 89.djvu/468

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��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.

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