RADIO SECTION 



Devoted to the Encouragement of Amateurs 



and Experimenters in the Field of 



Radio Communication 



Impedance of Oscillation Circuits 

 in Wireless Telegraphy 



By John Vincent 



IN last month's article it was shown 

 that every antenna had a particular 

 natural wave-length, or fundamental 

 wavelength, which it would radiate if it 

 were excited electrically and then left 

 to oscillate. It was pointed out that this 

 natural wavelength depended upon the 

 capacity and inductance of the aerial, 

 and that these in turn depended upon the 

 total length of the antenna-to-ground 

 system. It was also shown that if in- 

 ductance were added in series with the 

 antenna, so as to "load" the system elec- 

 tically, the resonant w^ave- 

 length would be increased. 

 A simple rule for comput- 

 ing arithmetically the reso- 

 nant radiant wavelength in 

 meters, when the capacity 

 in microfarads and the in- 

 ductance in millihenrys is 

 known, was stated. 



It should be noted espe- 

 cially that the wavelength 

 radiated depends upon the 

 size of the capacity and 

 inductance coils in the cir- 

 cuit. The reason for this 

 is that the length of radi- 

 ated wave depends upon its 

 frequency, or the number 

 of times in one second the 

 electromagnetic field ])ass- 

 cs through a complete cycle 

 of change in direction. 

 This wave-frequency must 



Fig. 1 



Fig. 2 



Kig. 



14: 



be the same as the frequency of the 

 oscillating current in the antenna system, 

 which produces it, and the oscillation 

 frequency is determined by the amount 

 of capacity and inductance in the anten- 

 na circuit. 



Considering ether-waves of the sort 

 used in radio-telegraphy, which pass 

 over the surface of the earth from the 

 sender to receivers in any direction at a 

 speed of 186,000 miles per second, the 

 usual relation between velocity, wave- 

 length and wave-frequency may be used. 

 In these waves, as in any 

 other traveling waves, the 

 frequency is found by di- 

 viding the velocity by the 

 wavelength. 



A wavelength of 2,000 

 meters has, therefore, a 

 w^ave-frequency of 150,- 

 000 per second, since the 

 velocity in meters per 

 second (300,000,000) di- 

 vided by the length (2,000 

 meters) gives this figure. 

 Thus, to find the frequen- 

 cy per second of any wave- 

 length in radio , divide 

 three hundred million by 

 the wavelength in meters. 

 Similarly, to find the wave- 

 length in meters for any 

 fre(|uency, divide the fre- 

 quency per second into 

 3 300,000,000, which goes: 



3 



