It is essential to make sure that both active rectifier circuits provide the same output voltages given the same input voltage, and an oscilloscope and sine wave function generator are necessary tools for this. Both active rectifier circuits should be originally constructed on a breadboard. R_F_2 and R_R_2 must match. (A value of 10,000 ohms is recommended initially.) A constant RF voltage of around 100mV 0-peak should be provided for V_F_0 and the DC voltage V_F_1 measured. The process should be repeated by providing the same RF voltage to V_R_0 and measuring V_R_1. For the same 100mV 0-peak RF voltages at V_F_0 and V_R_0, respectively, both V_F_1 and V_R_1 must have values within 1% of each other. Trial-and-error is needed to find two matching diodes, and it will take several tries to find a matching pair.
Once D_F_1 and D_R_1 are found, a matched pair of diodes for D_F_2 and D_R_2 must be found through a similar trial-and-error procedure. For the same 100mV 0-peak input at V_F_0 and V_R_0, the matched diodes D_F_1 and D_R_1 in place, and the matched resistors R_F_2 and R_R_2 in place, V_F_2 and V_R_2 should have measured DC voltages within 1% of each other. Again, trail-and-error is needed to find two matching diodes for D_F_2 and D_R_2.
Once D_F_2 and D_R_2 are found as well, it will be necessary to determine the optimum resistance value for matched resistors R_F_2 and R_R_2. With the two diode pairs in place, the optimum value for these two resistors can be determined. The matched diodes remain in place, but the RF input voltages are changed. Test the active rectifier circuit for input voltages in steps of a factor of 2 or less from 10mV to 10V. The input 0-peak voltages and the output DC voltages of the active rectifier should match to within about 10% of each other at all values from 100mV or higher and within about 30% of each other at all values from 40mV or higher. In some QROP units, the optimum resistance value will be 10,000 ohms. Other individual units will require a higher or lower resistance value. There is no way to know in advance what the optimal value will be.
WARNING: Watch your capacitor polarities.