I Amateur - 

 Electrician 



-And Wireless Operator 



Increasing the Efficiency of the 

 One-Inch Spark Coil 



THE more advanced amateur usually 

 turns his attention to power transmit- 

 ters, and consequently there is a lack of relia- 

 ble data applying to the small spark-coil 

 set. This necessarily works a hardship on 

 the beginner, whose initial equipment gen- 

 erally includes a spark coil. Therefore, a 

 few practical an- 

 swers to various 

 problems encoun- 

 tered in the opera- 

 tion of the popular 

 i-in. coil transmitter 

 should prove help- 

 ful not only to many 

 newcomers, but also 

 to more advanced 

 operators who are 

 troubled by inter- 

 ference from badly- 

 tuned small stations. 

 The writer has 

 raised the efficiency 

 of his i-in. coil 

 transmitter to a 

 point where he can 

 consistently outdis- 

 tance by more than 



The compact arrangement of the one-inch 

 spark coil when set upon the operator's table 



two miles any 2-in. coil in his vicinity, on a 

 power input of only 15 Watts. Specific 

 working directions for duplicating this set 

 will be given; but a few generalizations 

 must first be considered. 



It is a fallacy to suppose that the prin- 

 ciples governing the installation and tuning 

 of large sets do not apply to spark-coil 

 transmitters. The author is aware that 

 many beginners possessing small coils have 

 attempted to tune their stations but have 

 abandoned condenser and helix in disgust 

 after noting a considerable decrease in 

 sending radius. Little, if any, advantage 

 as to distance is to be gained by tuning sets 

 using coils smaller than ^ in., but larger 



transmitters become vastly more efficient 

 when properly adjusted. I have visited 

 many small stations that were not giving 

 satisfaction, and usually located the trouble 

 in the design or capacity of the trans- 

 mitting condenser, or discovered that 

 closed and open circuits were hopelessly 

 out of resonance. In one instance a 

 station was found to be using a condenser 

 consisting of sixteen 12 by 14-in. plates 

 across the secondary 

 terminals of a little 

 ij^-in. spark coil. 

 The spark discharge 

 was spectacular, yet 

 the range of the sta- 

 tion was less than 

 two miles. The er- 

 ror of regarding the 

 oscillation- trans- 

 former, or helix, as 

 a device to raise the 

 voltage of the high- 

 frequency currents 

 traversing the open 

 circuit seemed espe- 

 cially widespread. 

 The owners of the 

 stations had tuned 

 them by varying the 

 positions of thehelix 

 clips until sparks 3 or 4 in. long jumped a 

 gap inserted in the lead-in. Such evidence 

 should convince the skeptic that haphazard 

 application of the principle, not the princi- 

 ple itself, is responsible for the poor results 

 sometimes obtained by "tuning" a station 

 of this type. 



Tests have convinced me that in con- 

 nection with a spark-coil transmitter it is 

 best to use a conductively-coupled pancake 

 helix having a number of inductive turns 

 in both the primary and the secondary. 

 This necessitates the use of a transmitting 

 aerial not more than 40 ft. in length (T- 

 aerials excepted) with a lead-in not longer 

 than 30 ft., and a very small condenser in 



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