Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

NBC FREQUENCY-MODULATION FIELD TEST*tEaymond F.ByGuy and Robert M. MorrisNational Broadcasting Company, Inc., New YorkSummary—The full theoretical advantages of frequency modulation maybe obtained in practice if the transmitting and receiving apparatus are properlydesigned.For primary service, amplitude modulation on the ultra high frequenciesoffers some advantages over standard broadcasting. Frequency modulationoffers advantages over amplitude modulation on the ultra high frequencies.The advantages to the listener of frequency modulation on the ultra highfrequencies consist of freedom from the 10-kc beat note and side-band interferencewhich result from the frequency allocation of standard broadcasting,and also the reduction of locally generated noise, atmospherics, and interferencefrom distant stations operating on the same channel. Standardbroadcasting has the advantage of providing clear channel night-time serviceto vast areas which would not be served by frequency modulation on theultra high frequencies.TF~['pNjWENTY years ago allfrequencies above 1500 kc were generallyconsidered to be of such little value that even the amateurs hadobjections to being confined to them. There is no need to statehere what has since occurred on these "useless" frequencies nor to dwellon the fact that the surface has but been scratched. One service afteranother has wholly or partially transferred the bulk of its activitiesto them, and a multitude of new and invaluable services have been madepossible by their use. So-called "Standard Broadcasting" had a mosthumble beginning on 830 kc, which was then in the middle of themarine band of 500 kc to 1000 kc. Broadcasting quickly crowded theoriginal occupants out of most of this band.It is not one of the serviceswhich have since moved into the high-frequency spectrum.It remainson the former marine frequencies where it started. But there is apossibility that a shift may be approaching.The use of the ultra-high frequencies for sound broadcasting offerssome technical advantages. These advantages consist of escaping thepresent 10-kc channel limitation, getting away from static and eliminatingall except spasmodic long-distance interference. We haveknown this for many years, have for a decade experimentally operatedlow power u-h-f stations and at times have had the experience ofreceiving good service from our low-powered u-h-f transmitters whenstaticruined reception from our high-powered standard broadcastingplants. Five years ago the FCC had applications for, or had licensed,* Decimal Classification: R630 X R270.fReprinted from RCA REVIEW, October 1940.Ill