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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