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Page:Popular Science Monthly Volume 90.djvu/175

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What Radio Readers Want to Know

Interesting and Instructive Questions and Answers

��A 1500-mile Receiving Aerial; Loading Variometer

P. O. Pa., Baxley, asks:

Q. 1. Will No. 14 aluminum wire give about as good results as copper wire in an aerial comprising four wires 100 ft. in length. This aerial is intended for receiving purposes only, for distances of 1000 to 1500 miles from government and commercial stations.

A. 1. There will be no noticeable difference in strength of signals received on aluminum wire from those heard with copper aerial.

Q. 2. My inductively coupled receiving tuner in its present form has a maximum wavelength adjust- ment of 1500 meters; could I make it adjustable to 2500 meters by means of a variometer instead of the regulation type of loading coil?

A. 2. If the variometer is designed to have a sufficiently large maximum value of inductance it will ser\'e in every way as well as the simple cylindri- cal loading coil. In addition it will have the ad- vantage of continuous adjustment of inductance, as contrasted to tuning in steps. The best possible plan, however, would be to use a small variometer to allow close adjustment between the steps of inductance in your loading coil or transformer primary, and to make the large jump of inductance needed to go from 1500 to 2500 meters by use of a loading coil of the plain type, with a few large steps tapped off.

��Multiple-Layer Tuners for Large Value of Inductance

L. S. D., Fort Worth, Tex., writes:

Q. 1. Is it essential that the loading coils used in the undamped wave audion circuits be wound in a ■ingle layer on a very long spark to obtain the maximum degree of efficiency, or can they be wound in more than one layer on a core of short lei^th?

A. 1. Multi-layered coils have proven as efficient as the single-layer coil of great length provided the precaution is taken to separate the layers of the winding from ]/i in. to 3^^ in. By this method a coil of very small dimensions can be constructed for a very large value of inductance. In fact a coil i about 43^ in. in diameter and 6 in. in. length com- prising four layers of wire equals the inductance ] value of another coil 30 in. in length, 6 in. in diameter.

Q. 2. Where can I obtain cardboard tubes as a support for the windings of an inductively coupled receiving tuner to be 6 in. in diameter and 7 in. in diameter respectively?

A. 2. Tubing of these dimensions can be obtained from Ware & Company, Watt St., New York City.

��Charging an 800-foot Aerial with a Spark Coil; Intensifying Transformer

Dr. F. C. S., Gwinner, N. Dakota:

Q. 1. Will a 4 in. spark coil charge an aerial 800 ft. long, one wire, for sending; or what is the longest aerial it will charge regardless of wavelength?

A. 1. The longer the aerial wire the larger its capacity, and the more coulombs (quantity) of electricity are necessary to charge it to a given voltage. The output of a spark-coil depends upon so many other constants than its sparking length, especially when the coil is connected with a capacity such as an aerial, that it is impossible to answer your question specifically. The coil should charge the wire you mention to some potential high enough to produce a spark, but better results would doubtless be obtained with a shorter wire.

Q. 2. Can I use No. 36 wire which I have on hand, in building an intensifying transformer for use between two audions which are to be operated from the same batter^'?

A. 2. Yes, No. 36 wire can be used for the intensifying transformer windings. Make a core I in. in diameter by 6 in. long, and fit over it two spools having separation of i in. between flanges 4 in. in diameter. Wind each spool full of No. 36 double covered magnet wire, and immerse them in melted paraffin to fill the spaces and prevent damage by moisture. Slip the two filled spools over the core and place them side by side at the center. Either may be used as a primary coil, connected with the plate circuit of the first audion; the other then becomes the secondary and is connected with the grid circuit of the second audion. It is sometimes advantageous to connect only one terminal of the secondary with the grid of the second audion, leaving the other side of the coil open circuited. Which side to connect must be found by trial.

��Dimensions of a Transmitting Condenser and Coils

S. F., Whitewater, Wis., inquires:

Q. 1. Please state the dimensions for a mica dielectric condenser for a H K.W. transformer having a potential of 13,200 volts.

A. 1. We caution you not to construct a mica condenser unless you can obtain an extremely good grade of mica and have the necessary apparatus for impregnating the plates with an insulating com- pound. You would do better to purchase copper- plated Leyden jars.

Assuming that your set is to be operated at the wavelength of 200 meters the condenser should have a capacity of about .008 microfarads.

•^n oil-plate condenser for this purpose may

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