Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

86 FREQUENCY MODULATION, Volume Imore recent contribution 8 includes an experimental investigationchecking theory on the detection products produced in a frequencymodulation receiver. It is the purpose of this paper to report on develpmentwork undertaken by the engineering department of R.C.A.Communications, Inc.,wherein the propagation characteristics of frequencymodulation were determined for a circuitand New York.Early work done on frequency modulation within theRadio Corporationwas that of H. 0. Peterson 9between Californiain which a laboratory frequencymodulation circuit was set up. Later, in an attempt to reduce fadingby frequency diversity, one of the telegraph transmitters on the Argentinaand Brazil circuits was frequency modulated. Finally a definitedevelopment program was undertaken consisting of the developmentof a frequency modulation transmitter at the Rocky Point transmittingresearch and design laboratories and the development of a suitablereceiver at the Riverhead receiving research and design laboratories.After the transmitter and receiver were developed to a sufficientstage to permit a long-distance test to determine the propagation characteristicsof frequency modulation, the transmitter was shipped toBolinas, California, where it was operated by J. W. Conklin who hadassisted in its development. The transmissions were observed at theRiverhead station on the receivers developed by the author. The testswere carried out in1931 during the months from March to June, inclusive.Propagation TestsIn the tests carried on between Bolinas and Riverhead, two majorproblems presented themselves for solution.modulation withstand the ravages of fading.First, how would frequencySecond, could the detectedoutputs of two frequency-modulation receivers, fed by spaced antennas,be added directly 10 in a diversity 11 receiving system; that is, would thedetected audio outputs remain in phase so that they could be combineddirectly, or would some kind of diversity antenna choosing device,is in present use, be necessary.It is interesting to note that in this article Eckersley makes the followingprediction from his theory which agrees with the results obtained in thework described in this paper : "It will easily be seen that this results in mostappalling distortion, and renders futile any attempt to use even pure frequencymodulation in any transmission where appreciable echo delays (ofthe order of two or three milli-seconds) are present."8 J. G. Chaffee, "The detection of frequency modulated waves," Proc.I.R.E., vol. 23, pp. 517-540; May, (1935).9H. O. Peterson, U. S. Patent No. 1,789,371.10 C. W. Hansell, U. S. Patent No. 1,803,504.11H. O. Peterson, H. H. Beverage, and J. B. Moore, "Diversity telephonereceiving system of R.C.A. Communications, Inc.," Proc. I.R.E., vol.19, pp. 562-584; April, (1931).as