What Radio Readers Want to Know 



Interesting and Instructive Questions and Answers 



Construction of a Transformer; License 



for Experimental Station; Operation 



of Alternating Current Arc Sets 



E. D., St. Jdsoph, Mo., iiKjuircs: 



Q. 1. (Mease give the details of construction 

 for a i-K.\V. open core transformer and advise 

 how far I may expect to send with it? 



A. 1. .^n efficient transformer that will give a 

 secondary voltage of about 18,000 when con- 

 nected to a 6<)-cycle source of current supply may 

 l>e constructed in the following manner: Assem- 

 ble a core ,> in. in diameter, 2.s in. in length, com- 

 jiosed of a bundle of wires about \o. 30 B&S gage. 

 Care shouUl be taken to secure the best grade of 

 Norway iron. The core is then covered with 

 two layers of Empire cloth after which it is wound 

 with two layers of No. 10 U.C.C. wire, each layer 

 having 220 turns. The entire primary winding is 

 then inserted in a hard rubber or micanite tube 

 and proi>erly mounted on end supports. The 

 tube should have J-in. walls. 



The secondary winding is composed of a num- 

 ber of pancakes, the inside dimensions of which 

 are J in. greater than the primary tube. The 

 secondary winding is then composed of 38 sec- 

 tions, J in. in width, each pancake comprising 

 i,i2,s turns of No. 32 S.S.C. wire. Just previous 

 to the winding of the individual pancakes the 

 wire should be soaketl in hot paraffin. The pan- 

 cakes are of course separated by insulating 

 washers, such as fiber or hard rubber disks. This 

 transformer may be connected to (>o-cycle, no- 

 volt mains direct, without the insertion of a 

 |)rimary reactance coil. At the restricted wave 

 of 200 meters you will not be able to use the full 

 output of this transformer, as the required con- 

 denser for the secondary winding will have a 

 \alue of api)roximately .02 microfarads, which is 

 double the value that may be used at 200 meters. 

 This transformer should [wrmit a sending range of 

 50 to 100 miles during the daylight hours. 



Q. 2. Under what conditions can a license be 

 secured for the operation of an arc set for 

 undanipetl waves? 



A. 2. It is doubtful if the U. S. authorities 

 will issue a license certificate for an experimental 

 station of this type imless the license is requested 

 by an investigator of recognized standing whose 

 work may be of substantial benefit to the art. 

 \'ou had better address your inquiry to the Com- 

 missioner of Navigation, Washington, D. C, 

 slating the purpose for which you desire such 

 license. Also keep in mind that arc generators 

 do not operate well at wavelengths below 2,5t)o 

 meters, ("onseciuently you would be required to 

 operate your station at wavelengths that may 

 interfere with commercial traffic. 



Q. 3. How far will an arc set having J-in. 

 carbons connected to no volts alternating 

 current transmit? 



A. 3. Alternating current arc sets do not 

 operate satisfactorily and it is feared that you will 

 not be pleased with the results obtained. It is 

 the custom to use 500 to 1,500 volts direct cur- 

 rent, but good results can not be obtained by a 

 simple arc gap. The gap must be enclosed in a 

 chamber and fed with hydrogen or illuminating 

 gas and in addition blow-out magnets are mount- 

 ed at a right angle to the arc to increase the 

 difference of potential. The subject is fairly well 

 discussed in Zenneck's "Wireless Telegraphy." 



Audion Circuits of a "Beat" Receiver; 



Equipment for a 5 -Mile Range; 



Quenched and Rotary Gaps 



J. I. 1., Monroe, Mich., writes: 



Q. 1. Is it considered practical to use an 

 Audion or an Audiotron in the circuits of a '"beat" 

 receiver for wavelengths from spark stations lying 

 between 150 and 1000 meters? 



A. 1. Yes; but it is sometimes found difficult 

 to keep the Audion in oscillation at the lower 

 range of wavelengths. The circuits of the 

 De Poorest Ultraudion are said to overcome this 

 difficulty, but with other circuits better results 

 are secured at wavelengths in excess of 2,500 

 meters. The Ultraudion circuits are published 

 in the Proceedings of the Institute of Radio 

 Engineers. 



Q. 2. With an aerial 50 ft. in length, 20 ft. in 

 height and an earth wire 100 ft. in length, what 

 range could be expected from the follow ing instru- 

 ments? A 2-in. coil, 14- volt battery, suitable 

 condenser, small quenched gap and helix. The 

 foregoing apparatus is to transmit to a receiving 

 station comprising a tuning coil, galena detector, 

 2ooo-ohm receivers and con<lenser. 



A. 2. If the receiving apparatus is well de- 

 signed, you should be able to conmiunicate to a 

 distance of five miles provided local conditions do 

 not interfere. 



Q. 3. Is a quenched gap in series with a 

 rotary gap more efficient than the use of rotary 

 gap alone? 



A. 3. Generally, no; about the only value of 

 this combination is the fact that the rotary gap 

 allows one to obtain a high spark note from a 60- 

 cycle source of current supply. In a well- 

 designed set the quenched gap gives the greater 

 value of antenna current; but for ordinary 

 amateur working the rotary gap fulfills the re- 

 quirements. In the Clapp Eastham Hytone gap 

 the advantages of both types of spark dischargers 

 are combined in one construction. 



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