1 



HE 



DIG SECTION 



Devoted to the Encouragement of Amateurs 



and Experimenters in the Field of 



Radio Communication. 



An Improved Inductive Tuner 



By Charles Horton 



different types of couplers or 

 receiving transformers now in com- 

 mon use may be roughly divided into 

 classes as follows: 



(l) Couplers in which the adjustment in 

 coupling is obtained by sliding the secondary 

 within the primary. 



(2) Couplers in which the adjustment in 

 coupling is obtained by rotating the secondary 

 within the primary. 



In the first class may be included three 

 sub- types : 



(a) Those having slider adjustment on pri- 

 mary and slider adjustment on secondary. 



(&) Those having slider on primary and 

 switch adjustment on secondary and 



(c) Those having switch adjustment on 

 primary and switch adjustment on secondary. 



In the second class may be included 

 two sub-types, as follows: 



( a ) Those having sliders and 



(fr) Those having switches. 

 There are also a few other types which 

 may be classed as imperfect types of any 

 of the above, such as that type which has 

 neither primary nor secondary adjust- 

 ment, but relies entirely upon adjustable 

 condensers for tuning. 



All of the above types of couplers will 

 be found to have one or more of the 

 faults outlined below: 



(i) Presence of unused masses of wire giv- 

 ing rise to losses in efficiency. 



(2) Imperfect contacts causing resistance 

 and unreliability. 



(3) Dead ends causing imperfect tuning 

 qualities. 



It will be evident after consideration 

 that all of the above-mentioned types are 

 subject to one or more of the faults 

 enumerated, owing basically to the at- 



tempt to provide in one instrument a 

 multitude of combinations in order to be 

 able to receive on aerials of varying size 

 from many stations working on various 

 waves. Consequently, it will also be ap- 

 parent that much higher efficiency is ob- 

 tainable in the use of any particular aerial 

 by the use of a coupler wound particu- 

 larly for receiving from any particular 

 station. Thus, if it were possible for each 

 station to be provided with a number of 

 specially wound couplers in addition to 

 its adjustable coupler, accurate adjust- 

 ment for any station with which it was 

 in the habit of holding communication 

 would be merely a matter of connecting 

 its aerial and receiving circuits to the 

 particular coupler provided. The author 

 has long been of the opinion that just 

 such an arrangement will be the final 

 outcome of the present extensive ex- 

 perimentation in tuning, and has conse- 

 quently designed an apparatus embodying 

 this principle. This arrangement makes 

 it possible to be receiving from, say, 

 Nauen or Colon, or any other distant 

 station, and by the mere throwing of a 

 switch to connect with one's friend who 

 is calling, see what he has to say, and 

 by pimply throwing the switch back 

 again, to be in perfect tune as before 

 with the distant station. The inestimable 

 value of this apparatus will from the 

 above be readily apparent. The chief 

 objection to a set of this kind would 

 naturally be the high cost, but in this set 

 the cost is greatly reduced, and withal 

 a wonderfully perfect receiving set pro- 



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