Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

366 FREQUENCY MODULATION, Volume IThe construction of the transformer is evident from the photographin Figure 9.Slug tuning is used for both primary and secondarywindings. Since a bifilar construction is used for the secondary winding,the slug penetrates each half of the winding to essentially thesame degree, and hence variation in the position of the slug does notunbalance the two halves of the secondary winding.Even where theSecondary is capacitively tuned, this bifilar construction is desirablebecause it provides close coupling between the two halves of the secondaryand uniform coupling of each half of the secondary to theprimary winding.As shown in Figure 8, the major part of the rectified output voltageForm: 13/32" O.D. %" I.D. Bakelite XXXShield Can: 1%" Aluminum, SquareTuning Slugs: Stackpole G-2, SK-124Primary: 24 Turns #36E close woundTertiary: 4% Turns #36E close wound onlayer paper electrical tape (0.004) overB + end of primarySecondary: Bifilar, 18 Turns (total) #28.Form double grooved 20 TPI. Length ofwinding = 0.45"All windings counter clockwisestarting at far end* Measured adjacent to side rod Eis stabilized by means of the 8-microfarad condenser C 3. This, in con-tu>-Fig. 9—Details of construction of the ratio-detector transformer used inthe circuit of Figure 8. The bifilar secondary connections are brought outsymmetrically to the vertical rods to prevent unbalance.junction with the two diode load resistors R tand R 2 ,gives a dischargetime constant of approximately 0.1 second. The rectified voltage dropacross R 3 and R 4 is not stabilized against changes in diode current.This permits minimizing the residual balanced component of amplitudemodulation (See Figure 21) for this particular circuit design.The fact that the two resistors R s and R± are not equal in value makesit possible to produce a compensating unbalanced component whichcancels the unbalanced component which could otherwise appear in theoutput (see Figure 22). This unbalance is principally due to thevariation in the dynamic input reactance of the diodes and is not