Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

RATIO DETECTOR 359mdqJTAfPREQ DEVFig. 1—Basic circuit of a balanced discriminator. The output characteristicin (b) shows the dependence of the output on the input signal amplitude.tector insensitive to amplitude variations has been met by splittingthe rectified i-f voltages into two parts in such a way that the ratioof the rectified voltages is proportional to the ratio of the appliedfrequency-sensitive i-f voltages. It follows that if the sum of theserectified voltages is maintained constant by a suitable means, and iftheir ratio remains constant, the individual rectified voltages willalso remain constant. The output will therefore tend to be independentof amplitude variations in the input signal. A representative simplifiedratio-detector circuit is shown in Figure 2. The circuit connectionsare such that both diodes carry the same direct current. The rectifiedvoltages add to produce the sum voltage, which is held constant.The sum voltage may be stabilized by using a battery or by shunt-L /2Fig. 2—Basic circuit of a ratio detector using the same phase shift inputcircuit as in Figure 1. The rectified voltage is stabilized so that the outputcan be independent of the input amplitude.