Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

SUMMARIES — MISCELLANEOUS 505spiral-beam frequency control to this magnetron is considered in detail,and a procedure is presented for obtaining the optimum, design consistentwith negligible amplitude modulation and reasonable cathode-current densities.The unusual features of construction of this magnetron are described,including a, method of mechanical tuning and the method of adding gridcontrolledbeams for frequency modulation.Performance data on the continuous -wave magnetron over a wide rangeof operating conditions indicate that the required 25 watts output can beattained at 850 volts with 50 per cent efficiency. Experimental results on"spiral-beam" frequency control demonstrate that the required 2.5-megacyclefrequency deviation ivith no amplitude modulation can be achievedby electron beams introduced into two out of twelve cavities. A deviationof U megacycles is attained under conditions allowing some amplitudemodulation. Still greater deviation is predicted by using more beams.(8 pages; 10 figures)''Decimal Classification: R355.912M.f Proc. I.R.E., July, 1947.A 1-KILOWATT FREQUENCY-MODULATED MAGNE-TRON FOR 900 MEGACYCLES*!ByJ. S. Donal, Jr., R. R. Bush, C. L. Cuccia, and H. G. HegbarResearch Department. RCA Laboratories Division,Princeton, N. .1.SummaryThe method of Smith and Shulman has been used for the frequencymodulation of a 1-kilowatt continuous-wave magnetron. This tube is of the"Vane" type, having twelve resonant cavities, and it is mechanically tunableover a range from about 720 to 900 megacycles by a cylindrical elementwhich varies the interstrap capacitance. At the applied magnetic fieldrequired for frequency modulation without change in amplitude, 1 kiloivattoutput at 900 megacycles is obtained with an anode voltage of 2.5 kilovoltsand an efficiency of about 55 per cent; the efficiency rises with decreasingfrequency or with increasing magnetic field.At 900 megacycles, electron beams in nine of the magnetron resonantcavities give a frequency deviation of 3.5 megacycles (a total frequencyswing of 7 megacycles) at an output of 1 kilowatt, rising to h megacyclesat an output of 750 watts. The frequency deviation is reduced when the tubeis tuned to lower frequencies. The modulator power required would bevery low, since the grid-cathode capacitance of the frequency-modulationguns is small and the grids draw no current.It would be practicable to increase the frequency deviation of this tubeby about 15 per cent through an increase in beam current, and by an additional20 per cent through the use of eleven beams. A change in the typeof beam cathode would effect an even greater deviation.(6 pages; 6 figures; 1 table)* Decimal Classification: R355. 912.1.t Proc. I.R.E., July, 1947.