RADIO COMMUNICATION 255 



The rate of frequency of the vibrations set up in this cir- 

 cuit depends essentially on two factors, capacity and inductance. 

 The condenser furnishes the capacity, and the number of turns 

 used in the helix (coil) of the antenna circuit determines the 

 inductance. As we increase the number of turns of the helix 

 included in the antenna circuit, the greater inductance makes 

 the condenser accumulate a heavier charge before the discharge 

 occurs, so the intervals between discharges are longer and the 

 waves created are therefore longer. This arrangement makes it 

 possible to tune the sending station within limits depending upon 

 the size of the induction coil, condenser, length and height of 

 antenna, etc. Usually small amateur stations, are tuned so as to 

 have the maximum output of energy from the antenna within 

 government frequency regulations for amateur stations. 



The electrical vibrations which actually occur in the oscillat- 

 ing circuit and which are radiated into the ether from the antenna 

 are really a series of wave- trains. The more numerous the waves 

 are in each wave- train, the shorter each wave is; or the greater 

 the frequency, the shorter the wave-length. This frequency is 

 very high in radio waves, ranging from ten thousand up to several 

 million per second, and is known as radio frequency. Since the 

 waves travel in ether with the speed of light, or 300,000,000 meters 

 per second, we can easily determine the wave-length of a sending 

 station if we compute the frequency from the capacitance and 

 inductance values. Thus a frequency of 730 kilo-cycles (730,000) 

 would have a wave-length of about 411 meters. 



The rate at which the wave-trains succeed each other is 

 much lower than radio-frequency rates, and is within the range 

 of audio frequencies or the rate of vibration of sound waves, 

 usually around 500 to 1,000 cycles per second. The pitch or 

 note of the incoming wave from a damped wave-sending station 

 depends on the frequency of the wave-trains. Damped waves 

 are those that gradually die out like the waves of a wave-train 

 (Fig. 114). For comparison a standard A tuning fork vibrates 

 435 times* per second. 



