6 AUSTIN: HIGH SPARK FREQUENCY IN RADIO-TELEGRAPHY 



TABLE I 



STATIONS 



U. S. S. Salem 



Philadelphia Radio 

 New York Radio . . 

 Wilmington 



Baltimore 



Annapolis 



U. S. S. Delaware. 



6. « 



n ° 



to < 



H P5 



500 



500 

 500 



eo 



60 



60 



500 



D fa 

 H 0) 

 ■<! 

 8 



Z W 

 in « 



Fessenden 1£0 



rotary 

 Quenched 100 

 Quenched 190 

 Old type 80 ( 



fixed 

 Old type 35 



fixed 

 Old type 



fixed 

 Quenched 



> a w 



< Z £> 



1000 



2000 



2200 



600 



630 



600 



1000 



2 > h 



! — : h 

 o <• la 



fa fa 2 

 go* 



a 



mm. 



100 



220 

 20 

 65 



130 



70 



7 



Z H 

 fa H 



HP 



H ■< 



O H 



fa a 



W D 



77 



150 



18 



1.3 



1.45 

 1.1 



32 2.0 

 150 0.9 



93 



14 



8 

 0.5 



deflection on the galvanometer corresponds to the least audible 

 sound in the telephone. The sensibility of the galvanometer as 

 used was 1.3 10~ 9 amperes per millimeter. In the work with sine 

 waves already cited the telephones then used had a sensitiveness 

 of 3 X 10- 10 at 900 cycles and 3 X 10~ 7 amperes at 120 cycles. 

 These experiments were made in a perfectly quiet room and expe- 

 rience has shown that the amount of current necessary to distin- 

 guish the dots and dashes under ordinary conditions in the labor- 

 atory is roughly five times this. We may therefore take the 

 normal sensitiveness of these telephones for receiving purposes 

 as 1 . 5 . 10-° amperes at 900 cycles and 1.5.10" 6 at 120 cycles. 

 It is seen that the sensitiveness observed in the case of received 

 signals both at high and low frequencies in Table I corresponds 

 closely to the value obtained with sine waves at 900 cycles. This 

 seems to show conclusively that the higher degree of sensitive- 

 ness is obtained with practically all transformer sparks of the 

 types ordinarily used. 6 This might conceivably be explained 

 either by supposing that the sparks in low frequency apparatus 



6 Possibly sparks produced by induction coils with slow moving interrupters or 

 the infrequent sparks produced by certain forms of resonance transformers would 

 show a decreased telephone sensitiveness. 



