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CACD Group updated 2000.11.29 Author Janez Puhan |
Frequency DiscriminatorThe circuitWith amplitude modulation (AM), the information is contained within the instantaneous amplitudes in the high frequency carrier. With frequency modulation (FM), the information is hidden in the instantaneous deviation of frequency, while the amplitude remains constant. Circuits as described in previous case are not suited for the demodulation of frequency modulated carriers. A discriminator which converts frequency deviations into amplitude deviations has to be utilised. This could be a Bradley oscillator, a Foster-Seeley discriminator, or a ratio detector to name but a few. In the following example, an arrangement of two resonant circuits is shown. Depending on the coupling coefficients, k13 and k14, two resonant curves will occur side by side. Summation of these waveforms results in one double hump resonant curve. Subtraction, however, leads to a S-like discriminator characteristic where a more or less linear relationship between frequency and amplitude may be expected.
The input file
The results |
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