Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

362 FREQUENCY MODULATION, Volume 1Fig. 5—The voltages E u E*, Ei +Ei, E1-E2 which are present in Figure4(a) can be plotted as shown,with the aid of Figure 4(b).the stabilizing voltage to maintain E x + E 2constant has the effectof improving the linearity of the detector characteristic and extendingthe maximum deviation that can be handled for a given amount ofdistortion.The manner in which the ratio detector maintains a constant outputindependent of amplitude modulation may be seen by reference toFigure 6. If the amplitude of the input signal is constant as in (a),the stabilizing current is zero and the circuit has essentially the sameoutput characteristic as a balanced discriminator. On the other hand,if the input signal increases as in (b), the diodes are driven harder,the average diode current increases, and this increased direct currentflows into the stabilizing voltage source.Similarly, if the input signaldecreases, as in (c), the diode current decreases and the stabilizing(O) Conslon! normal input amplitude e p= e QStabilizing current i flDiode current iD =;E, + Ej^Tr^Effective diode load resistance = R + R((b) Increase in Input amplitude e p > eStabilizing current L B Rj+RjEffective diode lood resistance < R +(c) Decrease in input amplitude e P - E. + E,Diode current !„ < _! *R,+ R zEffective diode lood resistance >R +R,(Fig. 6—The effect of changes in input signal level on the diode current,the stabilizing current, and the effective load resistance presented to thediodes. The stabilizing voltage Ei + E2 is held constant at the voltage equalto the rectified output when e P = e».