Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

;Pig. 19—Relative amplification from thedriver grid to the secondary as a functionof the per cent of critical coupling, wherethe change in the per cent of criticalcoupling takes place as a result ofchanges in the primary or secondary Q.RATIO DETECTOR 377Circuit Impedance RatioThe ratio detector circuit may be put in the form shown in Figure20. Normally the input signal voltages e xand e 2 will follow theapproximate variation shown in Figure 5. These voltages may bederived from a phase-shift circuit, from side-tuned circuits, or fromother suitable means. A large number of circuit variations arepossible.If the circuit is analyzed from an impedance standpoint, it is foundthat the rectified voltages are in the same ratio as the input voltages,provided the circuit impedances z 1 and z 2 are in the same ratio as theinput voltages e ± and e 2.This can be demonstrated as follows. The diode currents flow inshort pulses, assuming ideal diodes, and therefore the fundamentala-c component of each diode current is nearly equal to twice the d-ccomponent. Since the d-c components are equal, it follows that thefundamental frequency a-c components will also be equal.i t = i 2iE x= k (e 1— izx ) and E 2= k (e 2— iz2 )EiE 2 e-> — iz2 e, / z 21-i —^_oe.Fig. 20—The ratio-detector circuit in a more general form. The voltagesei and e 2 may be produced in various ways, including the phase-shift circuitand side-tuned circuits.