Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

FREQUENCY MODULATION GENERATOR 107end of the tube. Electrical connections to the two electrodes of thetarget are brought out through this same seal.The spiral of this target was designed to give a maximum over-allphase shift of 360°—that is to say, for this particular target the value1of a in the equation r = a 8 is — inches per radian (the diameter ofITthe target is approximately four inches). In order to facilitate adjustmentand to judge operating performance four concentric circles andsixteen radial lines were marked on the surface of the target withwillemite. The entire surface of the target was also covered with avery thin coating of willemite. This results in the electron beamtracing out a visible path on the target, which is helpful in testing thetube.Pig. 6—Later form of the generator. The spiral anode makes five completeturns, and hence the degree of phase shift, for a given change in scanningradius, is proportionately increased.In constructing this tube the ftadiotron engineers made provisionfor utilizing secondary emission from the target anode to provide additionaloutput. This was done by providing a separate collector forsecondary electrons in the form of a coating on the inner wall of thetube.Figure 6 shows a photograph of a later model. The general designis the same except that the target anode consists of a conducting coatingdeposited directly upon the inner surface of the large end of thetube and the spiral in this case contains five complete cycles. The configurationof this target is shown by Figure 8.Figure 7 shows a schematic of the transmitter set-up employed totest the frequency modulator tube. That portion of the circuit enclosedby the upper dotted rectangle represents a conventional r-f transmitter.It was of the crystal-controlled type with buffer amplifiers and fre-