Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

FREQUENCY MODULATION GENERATOR 103anode, just as in the case of oscillograph tubes and picture tubes. Theelectron stream is sharply focused on the target anode and when thereis no voltage applied to the electrostatic deflecting plates it is adjustedto strike the exact geometrical center of the target anode. The inputs,which consist of two carrier waves of equal frequency and almost equalamplitude but differing in phase by 90° and having the same amplitudemodulation, are applied to the two sets of electrostatic deflecting plates.Figure 3 illustrates one means of supplying the inputs. The outputappears in the target anode circuit, across the impedance Z A. If Z A is apure resistance the output voltage appearing across it will be a flattoppedwave. By using a target anode composed of a larger number ofcurved sections the fundamental frequency of the flat-topped outputFig. 2—Typical target anode, consisting of two metal plates divided by apair of Archimedian spirals. The cathode ray beam scans the target in acircle of variable radius, producing square waves in the output.wave may be made any desired multiple of the input frequency. Thus itis seen that, if desired, frequency multiplication may be obtainedduring the process of converting amplitude modulation into frequencyor phase modulation.For a more detailed explanation of the way in which amplitudemodulation is translated into phase modulation, we refer now to Figure3. First, with no modulation, the phase shifting network and amplitudecontrols are adjusted so that the electron beam describes a circle on thetarget anode. If the master amplitude control is adjusted so that thiscircle is of the size designated by c x(Figure 2) then the voltageappearing across Z A will be as shown in Figure 4A. Note that the