Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

118 FREQUENCY MODULATION, Volume Ifeet above the sidewalk. Figure 6 shows the folded dipole in operatingposition.The circuit arrangement of the special 1000-watt transmitter isillustrated in the form of a block diagram in Figure 7. The frequencymodulator comprises the five blocks at the upper right side, containingRCA 6V6, 6K8 and 6H6 tubes.The degree of frequency deviation was measured by a methodrecently described in the RCA Review 2 . The method consists of applyinga constant frequency tone to the transmitter input terminals andgradually increasing the voltage until the carrier amplitude drops tozero. When this occurs, the frequency deviation is 2.405 times the audioFig. 4modulating frequency. This method is simple and very satisfactory ifreasonable precautions are taken.The ReceiversIn order that an exacting comparison of amplitude and frequencymodulation can be made, it is very desirable that the receivers forthe two systems be as nearly ideal and alike as possible.This practiceminimizes otherwise possible errors due to differences in receiver performance.The ideal way to build such receiving systems would be the2A Method of Measuring Frequency Deviation, M. G. Crosby, EGAReview, pp. 473-477, April, 1940.