Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

106 FREQUENCY MODULATION, Volume Iaround the outside of the main target facilitates adjustment of thephase shifting network to obtain circular deflection of the electronstream. Many other auxiliaries are possible.The description so far has related to the production of modulationin which the phase shift is directly proportional to the modulating voltage,but the system is quite flexible in this respect. By use of a properlyshaped target, the phase shift may be made any reasonable function ofthe modulating voltage, this being determined by the curvature of theedges of the target plates and the nature of the path traced on thetarget by the electron stream.The amplitude of the flat-topped output voltage wave may be variedindependently of the frequency (or phase) modulation by varying thed-c potential applied to the control grid. If it is desired to amplitudemodulate the output wave in addition to or instead of phase modulatingFig. 5—Early form of the cathode-ray frequency modulation generator,mounted in a standard oscilloscope tube envelope. The target anode is composedof spirals which make one complete turn.it in the manner described, this may be done readily by applying theamplitude modulation signal to the control grid, provided the electrongun is so operated that the rate of electron emission from the gun is alinear function of control grid voltage over the operating range.The photograph of Figure 5 shows the general appearance of anearly model of this device constructed by the Eadiotron Division of theRCA Manufacturing Co. It consists of a standard type cathode rayoscilloscope tube with a spiral target of the type specified above sealedinto the large end in place of the usual fluorescent screen. The targetwas constructed by applying a coating of platinum to a sheet of mica ofthe kind used for Iconoscope mosaics and scribing the separating linein the platinum surface to give the proper shape to the two electrodes.The target is mounted by wire supports which are sealed into the large