The tank circuit of a 0.5MHz LC oscillator has an inductance of 1mH connected across a capacitor. The output of this oscillator is frequency modulated by a FET reactance modulator consisting of a series connection of a 1500 Omega resistor and 10pF capacitor, with the capacitor connected between the gate-drain of the FET. The message signal varies the mutual conductance of the FET by +-0.6 mA/ volt, finding the peak frequency deviation that is produced.

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To find the peak frequency deviation produced by the FET reactance modulatorwe can use the following formula f fc gm V where f is the peak frequency deviation in Hz fc is the carrier frequency in Hz gm is the mutual conductance of the FET in mAV V is the change in gate voltage in V In this casewe have fc 05 MHz 500 kHz gm 06 mAV V 1 V assuming that the message signal varies the gate voltage by 1 V Substituting these values into the formulawe get f 500 kHz 06 mAV 1 V 300 Hz Therefore the peak frequency deviation produced by the FET reactance modulator ... View the full answer