Popular Science Monthly 



635 



There is no need of any rectifying 

 crystal or other complex conducting 

 system if the incoming oscillations are 

 passed through a high-speed commuta- 

 tor. The tone- wheel, formerly used at 

 the Tuckerton Transatlantic Station, 

 is an apparatus whose operation has 

 been described as mechanical rectifica- 

 tion. A nearly identical device is shown 

 in U. S. Patent 1,172,017, which w^as 

 applied for by R. A. Fessenden in 1906 

 and was issued during the past year. 

 The drawing indicates an antenna I 

 connected to earth 2 through a primary 

 inductance 17, which serves both to 

 tune the aerial system and to couple that 

 circuit with the secondary coil 18. The 

 upper terminal of 18 leads to a rotating 

 contact arm 5 which passes at high 

 speed over segments 7, 8 of a large 

 commutator. The lower secondary con- 

 nection is taken through a telephone 20 

 and the wire 37 to the group of alternate 

 segments marked 8 and connected to- 



[ gether through 8a. 



I If the brush 5 is rotated at a high rate 



it is possible to secure synchronism 

 betv^een the time of contact and the 



k alternations of the received-wave cur- 

 rents. By arranging matters so that the 

 rotating contactor rests upon a segment 

 of the No. 7 group during each negative 

 half- wave of received current and upon 

 a No. 8 segment throughout each 

 positive half-wave, a positive direct 

 current will flow through the telephone 

 whenever waves are received. Thus the 

 system acts mechanically to convert the 

 radio-frequency alternating current into 

 direct current suitable for producing 

 telephonic effects if interrupted. As 

 shown in the diagram, only one-half of 

 the wave-current is used ; by connecting 

 another ear-piece, such as 20, to the 

 remaining group of segments (No. 7) 

 and carrying the circuit to the lower 

 end of 18, both halves will be made 

 eflfectiv'e. 



When receiving sustained waves it is 

 merely necessary to run the commutating 

 contact at a speed slightly different 

 from synchronism, if a musical note is 

 desired. The interruptions then gradu- 

 ally change in relation to the half-waves, 

 so that for a time the rectification is 

 positive and then for a time negative. 

 The rapidity of change of rectification 

 polarity depends upon the difference 

 between the interruption frequency and 

 that of the waves. 



Making an Inclosed Rotary 

 Spark Gap 



SEVERAL enclosed gaps such as are 

 herein described hav'e been made 

 by the writer and have not only proved 

 very efficient but also have reduced the 

 noise of the spark a great deal. 



The dimensions given in this article 



The rotor is made from an aluminum zinc 

 combination casting to prevent wearing 



are of course applicable only to one size 

 motor and may have to be changed. If 

 the amateur has no motor, one of about 

 i/io horsepower, which is either induc- 

 tion or series wound, should be procured, 

 as this power will allow for a larger and 

 more accurate rotor. If an induction 

 motor is used, the number of points or 

 lugs on the rotor should be such that it 

 will give a frequency of any odd multiple 

 of 120, such as 360, 600, 840 or 1080 

 sparks per second. This will give a clear 

 note or 60 cycles without any undertone. 

 The rotor (Fig. i), is made from an 

 aluminum zinc combination casting, as 



'•^^8 





Uf-t 



^ 



1 © S ^cs 



I 6 laps] ^^ H 



FIG 2 



Dimensions of the parts required for at- 

 taching the handles to the spark-gap frame 



this will not wear away very fast and is 

 easy to work. Pure copper can also be 

 used if one has a motor of }/% horse- 



