Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

I272 FREQUENCY MODULATION, Volume Iespecially for the entire adjacent channel, is shown with the receiveremploying the frequency-dividing locked-in oscillator system. It shouldbe noted that with an increase in interfering signal, a point of oscillatorbreakout may always be reached. The level of interfering signal atwhich breakout occurs is higher than the — 30-decibel interferencelevel. The improvement in adjacent-channel selectivity, shown by thesecurves, is equivalent to the addition of two intermediate-frequencystages in the receiver.TWO SIGNAL SELECTIVITYDESIRED SIGNAL IOO/"V.INTERFERING SIGNAL ADJUSTED FOR -30 DB INTERFERENCE:"A"«LOCKED-IN OSCILLATOR'•UNMODIFIED RECEIVER.10,000ipoo100300 200MODULATIONJ LMTTSOTADJACENT"I CHANNEL jIH\TsVKl 10100 100 200 300KC SEPARATIONPig. 17—Selectivity curves.Impulse Noise InterferenceOscilloscopic investigations of the effects of impulse interferencewith both modulated and unmodulated signals were made with the fourreceivers. The results indicated a general superiority in noise reductionfor the frequency-dividing locked-in oscillator system.Field TestsField tests showed the receivers using the new receiving system