Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

RATIO DETECTOR 365this type of detector tend to be quiet between stations. When a-v-cis used, the selectivity of the receiver is maintained for strong aswell as weak signals.The tuning characteristic of a receiver using the ratio detector ischaracterized by comparatively low side responses. This results, inpart, because the high degree of amplitude modulation which an offresonantf-m signal acquires as it is modulated up and down the steepi-f selectivity curve produces relatively little output from the ratiodetector. The extent to which the side responses will fall below themain response depends upon the amount of a-v-c, the i-f selectivity,and the ratio-detector peak separation.Typical Ratio DetectorThe circuit and performance data for a ratio detector circuit oper-J_ 2000R 6~C 5— DEEMPHASIS CIRCUITPig. g—A ratio-detector circuit using a balanced phase shift transformerfeeding a 6AL5 double diode. The closely coupled tertiary winding Lt iswound over the B+ end of the primary to provide impedance matchingand improved sensitivity.ating at a center frequency of 10.7 megacycles is shown in Figure 8.In order to improve the sensitivity, a form of impedance matching isused between the high impedance of the driving pentode and the relativelylow impedance which the diodes reflect across the winding thatinjects the primary voltage into the diode circuit. This is, of course,the winding L twhich is wound over the cold end of the primarywinding L pand is tightly coupled to the primary. The phase of thevoltages across L pand L, is therefore substantially the same. Thevoltages across L tand L sare in quadrature (at the center frequency)and in accordance with the action which has been previously described,the demodulated f-m output is taken off through a connection to thesecondary winding.