Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

RATIO DETECTOR 369Half-secondary/tertiary voltage ratio: 0.65Coupling: 0.50 of critical. (This includes the effect of the capacitanceunbalance due to the difference between the inputcapacitances of the two diodes.)Grid-to-plate gain : The normal gain is 100. (Under the conditionsyielding maximum gain, i.e., with downwardamplitude modulation off the center frequency,the grid-plate gain rises to 130.)Circuit AnalysisThe analysis of the ratio detector is more difficult than that of the100O MV INPUTFig. 12—The demodulated output when an f-m signal, 75 kilocycles deviation,having simultaneous a-m modulation, is applied to the ratio detectorin Figure 8. The f-m modulation is at 400 cycles; the a-m modulation is at250 cycles. The width of the detector characteristic indicates the residuala-m output.balanced discriminator primarily because of the variation in equivalentload resistance during the a-m cycle as well as during the f-mcycle. In addition, the problem is complicated by the complex impedancecharacteristics of the frequency-sensitive driving circuit, thenon-linearity of the diode characteristics, and the input reactancevariations of the diodes which tend to modify the frequency characteristicof the driving circuit. A productive method of attack is toconsider firstthe equivalent circuit and to develop an expression forthe ratio of primary and secondary voltage. This expression is impor-