Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

RATIO DETECTOR 367necessarily an indication that the circuit itself is unbalanced in anyway. The 47-ohm resistor R 6modifies the peak diode currents andfurther reduces thesignal levels.unbalanced a-m component, particularly at highThe condenser C 4 bypasses the secondary system to ground at theintermediate frequency. The conventional deemphasis circuit whichis conveniently placed at this point provides further filtering againsti-f getting into other circuits and causing feedback. A 39,000-ohmresistor and a 0.002-microfarad condenser are suitable values for thedeemphasis circuit.The alignment procedure for this detector consists of applying anunmodulated i-f signal to the ratio-detector driver tube and peakingPig. 10—Output characteristic and performance data for the ratio detectorshown in Figure 8. Input signal = 100 millivolts; Rectified voltage = 6volts; A-V-C voltage = 2.5 volts; A-P output (75-kilocycle deviation) =0.7volt root-mean-square; Distortion (100 per cent modulation) = 2.5 per centroot-mean-square; Distortion (30 per cent modulation) =0.7 per cent rootmean-square;Maximum downward amplitude modulation = 70 per cent.the primary so that maximum rectified voltage is obtained, as indicatedby a d-c voltmeter connected to the a-v-c takeoff point(Figure8). The secondary tuning is then adjusted for zero voltage as indicatedby a d-c voltmeter connected to measure the voltage at the audiotake-off point. It will be noted that the alignment procedure is essentiallythe same as for a balanced discriminator.Because the primaryand secondary windings are below critical coupling, there is negligibleinteraction between the adjustments.The output characteristic of this detector is shown in Figure 10,along with the data giving the audio recovery and rectified voltagefor 100 millivolts input to the last i-f tube, i.e., to the ratio-detector