Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

110 FREQUENCY MODULATION, Volume Ito the grid of an amplifier which in turn fed a frequency doubler.Thesucceeding stage fed a shielded r-f transmission line, the other end ofwhich was coupled to the 860 stage in the transmitter which ordinarilyoperated as a doubler but which was used as a straight amplifier in thiscase. From that point on the various stages of the transmitter wereoperated in their usual manner.The transmitter was located in the Empire State Building andreception tests were made with a frequency modulation receiver locatedin the Development Laboratory in Kadio City. These tests showed thatthe cathode ray frequency modulator performed as predicted. Whenproperly shielded against stray magnetic fields and provided with wellfilteredd-c potentials, it introduced no measurable distortion and wasperfectly stable in its operation.In conclusion, acknowledgment is made of the cooperation of theRCA Radiotron Laboratories in constructing and supplying the tubesused in these tests and of the helpful suggestions offered by Radiotronand NBC engineers. The author also wishes to acknowledge with deepappreciation the encouragement and cooperation extended by ProfessorE. H. Armstrong of Columbia University during the. early tests onthis device.