. The principles underlying radio communication . reater than a value ofslightly above 100,000 cycles, while below that point it has thecharacter of a capacitive reactance. Furthermore for only anarrow range of frequencies, 99,000 to 103,000, perhaps, thereactance of the circuit is less than 10 ohms. For most fre-quencies the reactance is much greater than this. The frequency which makes the capacitive and inductive re-actances equal is called the resonance frequency of the cir-cuit, and the circuit is said to be in resonance, or to be** tuned to the frequency in question. It is important to b
. The principles underlying radio communication . reater than a value ofslightly above 100,000 cycles, while below that point it has thecharacter of a capacitive reactance. Furthermore for only anarrow range of frequencies, 99,000 to 103,000, perhaps, thereactance of the circuit is less than 10 ohms. For most fre-quencies the reactance is much greater than this. The frequency which makes the capacitive and inductive re-actances equal is called the resonance frequency of the cir-cuit, and the circuit is said to be in resonance, or to be** tuned to the frequency in question. It is important to beable to calculate the frequency for resonance. To do so, thecondition must be fulfilled, that 2^//^=^ (70) 27r/C which shows that the frequency at resonance must be /= o ^ (71) Applying this relation to the example under discussion, andsubstituting therein L= henry, C=iq9 farad, the reso-nance frequency is found to be about 100,700 cycles per reactances of both the coil and the condenser at this fre- 236 RADIO CIRCUITS. &00. -60<fi- ^3- sdooo 100000 ISOOOQ 200000 &SOOO0 lOOOOO Frequencu—cycles per second. 133. Variation of reactance with Freqaencu. / •=■ soo microhenriesC - COOS microfarads
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